This doesn't quite get all the way there, but the failure is being caused by the closure of a _io.FileIO due to GC, which happens to have the same fd as the sqlite database. The closure happens in the middle of a SQLite operation, which causes a subsequent flock() call to fail.

strace log from the failure:

open("/home/travis/apprise-api/.coverage", O_RDWR|O_CREAT|O_CLOEXEC, 0644) = 31
fstat(31, {st_mode=S_IFREG|0644, st_size=192512, ...}) = 0
fstat(31, {st_mode=S_IFREG|0644, st_size=192512, ...}) = 0
lseek(31, 0, SEEK_SET) = 0
read(31, "SQLite format 3\0\4\0\1\1\0@ \0\0\0\n\0\0\0\274"..., 100) = 100
write(3, "00001299 0001 6169 execute('prag"..., 54) = 54
write(3, "Executing 'pragma journal_mode=o"..., 36) = 36
write(3, "self: <SqliteDb @0x7fa0feef9fd0 "..., 86) = 86
fcntl(31, F_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1073741824, l_len=1}) = 0
fcntl(31, F_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1073741826, l_len=510}) = 0
fcntl(31, F_SETLK, {l_type=F_UNLCK, l_whence=SEEK_SET, l_start=1073741824, l_len=1}) = 0
fstat(31, {st_mode=S_IFREG|0644, st_size=192512, ...}) = 0
fstat(31, {st_mode=S_IFREG|0644, st_size=192512, ...}) = 0
lseek(31, 0, SEEK_SET) = 0
read(31, "SQLite format 3\0\4\0\1\1\0@ \0\0\0\n\0\0\0\274"..., 1024) = 1024
lseek(31, 8192, SEEK_SET) = 8192
read(31, "\r\3-\0\4\0\316\0\3^\1X\0035\0\316\0\245\0v\0v\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024
lseek(31, 9216, SEEK_SET) = 9216
read(31, "\r\0\0\0\4\0\370\0\0\370\3d\0035\1!\0\277\0\277\2\36\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024
lseek(31, 14336, SEEK_SET) = 14336
read(31, "\r\0\0\0\4\0\320\0\3\315\1\313\1\244\0\320\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024
fcntl(31, F_SETLK, {l_type=F_UNLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = 0
write(3, "00001299 0001 6169 execute retur"..., 76) = 76
write(3, "00001299 0001 6170 execute('prag"..., 53) = 53
write(3, "Executing 'pragma synchronous=of"..., 35) = 35
lseek(31, 0, SEEK_CUR) = 15360
close(31) = 0
write(3, "self: <SqliteDb @0x7fa0feef9fd0 "..., 86) = 86
write(3, "00001299 0001 6170 execute retur"..., 76) = 76
write(3, "00001299 0001 6168 _connect retu"..., 40) = 40
write(3, "00001299 0001 6167 __enter__ ret"..., 116) = 116
write(3, "00001299 0001 6171 execute('sele"..., 82) = 82
write(3, "Executing 'select tracer from tr"..., 68) = 68
write(3, "self: <SqliteDb @0x7fa0feef9fd0 "..., 86) = 86
fcntl(31, F_SETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1073741824, l_len=1}) = -1 EBADF (Bad file descriptor)
open("/home/travis/apprise-api/.coverage", O_RDONLY|O_CLOEXEC) = 31
fstat(31, {st_mode=S_IFREG|0644, st_size=192512, ...}) = 0
ioctl(31, TCGETS, 0x7fff3bfa4920) = -1 ENOTTY (Inappropriate ioctl for device)
lseek(31, 0, SEEK_CUR) = 0
read(31, "SQLite format 3\0\4\0\1\1\0@ \0\0\0\n\0\0\0\274"..., 4096) = 4096
close(31) = 0
write(3, "EXCEPTION from execute: disk I/O"..., 39) = 39
write(3, "self: <SqliteDb @0x7fa0feef9fd0 "..., 86) = 86
write(3, "00001299 0001 6172 __exit__(<cla"..., 208) = 208
write(3, "00001299 0001 6173 close()\n", 27) = 27
fstat(31, 0x7fff3bfa4220) = -1 EBADF (Bad file descriptor)
close(31) = -1 EBADF (Bad file descriptor)

Notice the close(31) right after the lseek. This close(31) is not generated by SQLite; rather, it's being generated by the GC finalization of an unrelated file object:

#0 internal_close (self=<optimized out>) at ./Modules/_io/fileio.c:126
#1 _io_FileIO_close_impl (self=<optimized out>) at ./Modules/_io/fileio.c:171
#2 _io_FileIO_close (self=<optimized out>, _unused_ignored=<optimized out>) at ./Modules/_io/clinic/fileio.c.h:23
#3 0x00007ffff7975be7 in _PyCFunction_FastCallDict (func_obj=func_obj@entry=0x7fffeefaee58, args=args@entry=0x7fffffff7590, nargs=0, kwargs=kwargs@entry=0x0) at Objects/methodobject.c:192
#4 0x00007ffff791b89e in _PyObject_FastCallDict (func=func@entry=0x7fffeefaee58, args=args@entry=0x7fffffff7590, nargs=<optimized out>, kwargs=kwargs@entry=0x0) at Objects/abstract.c:2313
#5 0x00007ffff791c8a4 in PyObject_CallMethodObjArgs (callable=0x7fffeefaee58, name=<optimized out>) at Objects/abstract.c:2759
#6 0x00007ffff7a976b4 in buffered_close (self=0x7fffee02ae08, args=<optimized out>) at ./Modules/_io/bufferedio.c:538
#7 0x00007ffff7975be7 in _PyCFunction_FastCallDict (func_obj=func_obj@entry=0x7fffedf7eab0, args=args@entry=0x7fffffff77c0, nargs=0, kwargs=kwargs@entry=0x0) at Objects/methodobject.c:192
#8 0x00007ffff791b89e in _PyObject_FastCallDict (func=func@entry=0x7fffedf7eab0, args=args@entry=0x7fffffff77c0, nargs=<optimized out>, kwargs=kwargs@entry=0x0) at Objects/abstract.c:2313
#9 0x00007ffff791c8a4 in PyObject_CallMethodObjArgs (callable=0x7fffedf7eab0, callable@entry=0x7fffee02ae08, name=<optimized out>) at Objects/abstract.c:2759
#10 0x00007ffff7a90def in iobase_finalize (self=0x7fffee02ae08) at ./Modules/_io/iobase.c:266
#11 0x00007ffff7a59e4f in finalize_garbage (collectable=0x7fffffff7950) at Modules/gcmodule.c:806
#12 collect (generation=generation@entry=1, n_collected=n_collected@entry=0x7fffffff79f0, n_uncollectable=n_uncollectable@entry=0x7fffffff79f8, nofail=nofail@entry=0) at Modules/gcmodule.c:1005
#13 0x00007ffff7a5a63b in collect_with_callback (generation=1) at Modules/gcmodule.c:1128
#14 0x00007ffff7a5ae8b in collect_generations () at Modules/gcmodule.c:1151
#15 _PyObject_GC_Alloc (basicsize=<optimized out>, use_calloc=0) at Modules/gcmodule.c:1729
#16 _PyObject_GC_Malloc (basicsize=<optimized out>) at Modules/gcmodule.c:1739
#17 0x00007ffff7a5afdd in _PyObject_GC_New (tp=tp@entry=0x7ffff7d53ea0 <PyGen_Type>) at Modules/gcmodule.c:1751
#18 0x00007ffff794766f in gen_new_with_qualname (qualname=0x7ffff4c1b450, name=0x7ffff4c218f0, f=0x7ffff292daf8, type=0x7ffff7d53ea0 <PyGen_Type>) at Objects/genobject.c:802
#19 PyGen_NewWithQualName (f=0x7ffff292daf8, name=0x7ffff4c218f0, qualname=0x7ffff4c1b450) at Objects/genobject.c:830
#20 0x00007ffff7a07f31 in _PyEval_EvalCodeWithName (_co=0x7ffff4c23270, globals=globals@entry=0x7ffff4cdd9d8, locals=locals@entry=0x0, args=<optimized out>, argcount=1, kwnames=kwnames@entry=0x0, kwargs=0x7ffff4c32930,
kwcount=0, kwstep=1, defs=0x0, defcount=0, kwdefs=0x0, closure=0x7fffede2cfd0, name=0x7ffff4c218f0, qualname=0x7ffff4c1b450) at Python/ceval.c:4150
#21 0x00007ffff7a081d7 in fast_function (kwnames=0x0, nargs=<optimized out>, stack=<optimized out>, func=0x7fffedc03f28) at Python/ceval.c:4978
#22 call_function (pp_stack=pp_stack@entry=0x7fffffff7c60, oparg=oparg@entry=1, kwnames=kwnames@entry=0x0) at Python/ceval.c:4858
#23 0x00007ffff7a0a633 in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3335

Note that normal SQLite3 closes look like this:

#0 0x00007ffff769b560 in __close_nocancel () from /lib/x86_64-linux-gnu/libpthread.so.0
#1 0x00007ffff3a23d8c in robust_close (lineno=29378, h=<optimized out>, pFile=0x113cfd8) at sqlite3.c:28631
#2 closeUnixFile (id=id@entry=0x113cfd8) at sqlite3.c:29378
#3 0x00007ffff3a24f43 in unixClose (id=0x113cfd8) at sqlite3.c:29427
#4 0x00007ffff3a4858b in sqlite3OsClose (pId=0x113cfd8) at sqlite3.c:17944
#5 sqlite3PagerClose (pPager=0x113ce68) at sqlite3.c:47961
#6 0x00007ffff3a5930b in sqlite3BtreeClose (p=0xfb8088) at sqlite3.c:58266
#7 0x00007ffff3a59501 in sqlite3LeaveMutexAndCloseZombie (db=0x1260598) at sqlite3.c:134102
#8 0x00007ffff3a59ae2 in sqlite3Close (db=0x1260598, forceZombie=0) at sqlite3.c:134045
#9 0x00007ffff3cc8fe2 in pysqlite_connection_close (self=0x7fffedf5fd50, args=<optimized out>) at /tmp/python-build.20181021062245.3423/Python-3.6.7/Modules/_sqlite/connection.c:337
#10 0x00007ffff7975be7 in _PyCFunction_FastCallDict (func_obj=0x7fffedf7eab0, args=0x7fffede2e890, nargs=0, kwargs=kwargs@entry=0x0) at Objects/methodobject.c:192
#11 0x00007ffff7975eb7 in _PyCFunction_FastCallKeywords (func=func@entry=0x7fffedf7eab0, stack=stack@entry=0x7fffede2e890, nargs=<optimized out>, kwnames=kwnames@entry=0x0) at Objects/methodobject.c:294
#12 0x00007ffff7a082c1 in call_function (pp_stack=pp_stack@entry=0x7fffffff9640, oparg=oparg@entry=0, kwnames=kwnames@entry=0x0) at Python/ceval.c:4837

EDIT 1: OK, I found the line of code that allocates this file, at line 398 in apprise_api/api/views.py:

with NamedTemporaryFile() as f:
# Write our content to disk
f.write(config.encode())
f.flush()

If you disable this block of code everything runs fine (although the tests fail). It's kinda creepy that the NamedTemporaryFile is leaking - it really shouldn't...