[G3 Q&A, Help & Troubleshooting] waspish_ly:
The second kdz flash took less than five minutes. The first one, that worked took enough time for two cups of coffee, a sandwich and then some. The first time, things like RECOVERY, SYSTEM, etc. appeared on the progress bar. I'm assuming that was it flashing those partitions.

The second time, none of that happened, it went straight from connecting, then some weird code, then straight to waiting for 120s, at which point the phone rebooted. I tried and had the same result on two different PCs.

And what exactly does 'bootable' entail? LineageOS installed successfully, I can mount the partition and on a cursory glance everything looks okay.

Additionally, I just took a dump of all the partitions on it. Some of the files have size zero, and I'm a bit worried. The folder listing looks like this:

total 15G
drwxr-xr-x 2 user user 4.0K Jan 29 17:13 .
drwxr-xr-x 3 user user 4.0K Jan 29 16:16 ..
-rw-r--r-- 1 user user 2.1M Jan 29 16:24 aboot
-rw-r--r-- 1 user user 2.0M Jan 29 17:02 abootf
-rw-r--r-- 1 user user 17M Jan 29 17:02 boot
-rw-r--r-- 1 user user 609M Jan 29 17:13 cache
-rw-r--r-- 1 user user 180M Jan 29 17:14 cust
-rw-r--r-- 1 user user 513K Jan 29 16:23 dbi
-rw-r--r-- 1 user user 513K Jan 29 16:24 dbibak
-rw-r--r-- 1 user user 512K Jan 29 16:23 DDR
-rw-r--r-- 1 user user 8.1M Jan 29 17:02 drm
-rwxr-xr-x 1 user user 2.9K Jan 29 16:22 dump-parts.sh
-rw-r--r-- 1 user user 512K Jan 29 17:02 eksst
-rw-r--r-- 1 user user 512K Jan 29 17:14 encrypt
-rw-r--r-- 1 user user 0 Jan 29 16:23 factory
-rw-r--r-- 1 user user 33M Jan 29 16:23 fota
-rw-r--r-- 1 user user 512K Jan 29 16:24 fsc
-rw-r--r-- 1 user user 3.0M Jan 29 17:02 fsg
-rw-r--r-- 1 user user 20M Jan 29 17:02 grow
-rw-r--r-- 1 user user 33M Jan 29 17:14 laf
-rw-r--r-- 1 user user 0 Jan 29 16:23 misc
-rw-r--r-- 1 user user 65M Jan 29 16:23 modem
-rw-r--r-- 1 user user 3.1M Jan 29 16:24 modemst1
-rw-r--r-- 1 user user 3.1M Jan 29 17:02 modemst2
-rw-r--r-- 1 user user 33M Jan 29 17:02 mpt
-rw-r--r-- 1 user user 4.0K Jan 29 17:14 pad
-rw-r--r-- 1 user user 0 Jan 29 16:23 pad1
-rw-r--r-- 1 user user 4.0K Jan 29 16:23 pad2
-rw-r--r-- 1 user user 33M Jan 29 16:24 persist
-rw-r--r-- 1 user user 8.0K Jan 29 17:02 rct
-rw-r--r-- 1 user user 17M Jan 29 17:03 recovery
-rw-r--r-- 1 user user 1.1M Jan 29 17:14 rpm
-rw-r--r-- 1 user user 0 Jan 29 16:23 rpmbak
-rw-r--r-- 1 user user 1.0M Jan 29 16:23 rpmf
-rw-r--r-- 1 user user 1.1M Jan 29 16:24 sbl1
-rw-r--r-- 1 user user 1.1M Jan 29 17:02 sbl1b
-rw-r--r-- 1 user user 512K Jan 29 17:03 sdif
-rw-r--r-- 1 user user 8.1M Jan 29 17:14 sns
-rw-r--r-- 1 user user 0 Jan 29 16:23 spare1
-rw-r--r-- 1 user user 5.0M Jan 29 16:24 spare2
-rw-r--r-- 1 user user 16M Jan 29 16:24 spare3
-rw-r--r-- 1 user user 512K Jan 29 17:02 ssd
-rw-r--r-- 1 user user 2.1G Jan 29 17:12 system
-rw-r--r-- 1 user user 1.1M Jan 29 17:14 tz
-rw-r--r-- 1 user user 0 Jan 29 16:23 tzbak
-rw-r--r-- 1 user user 1.0M Jan 29 16:24 tzf
-rw-r--r-- 1 user user 12G Jan 29 17:02 userdata

And the fdisk listing from a shell on the phone is:

fdisk -l /dev/block/mmcblk0
Found valid GPT with protective MBR; using GPT

Disk /dev/block/mmcblk0: 30777344 sectors, 2740M
Logical sector size: 512
Disk identifier (GUID): 98101b32-bbe2-4bf2-a06e-2bb33d000c20
Partition table holds up to 44 entries
First usable sector is 34, last usable sector is 30777310

Number Start (sector) End (sector) Size Code Name
1 32768 163839 64.0M 0700 modem
2 163840 165887 1024K 0700 sbl1
3 165888 166911 512K 0700 dbi
4 166912 167935 512K 0700 DDR
5 167936 172031 2048K 0700 aboot
6 172032 174079 1024K 0700 rpm
7 174080 176127 1024K 0700 tz
8 176128 176135 4096 0700 pad
9 176136 178183 1024K 0700 sbl1b
10 178184 179207 512K 0700 dbibak
11 179208 181255 1024K 0700 rpmbak
12 181256 183303 1024K 0700 tzbak
13 183304 185351 1024K 0700 rpmf
14 185352 187399 1024K 0700 tzf
15 187400 188423 512K 0700 sdif
16 188424 192519 2048K 0700 abootf
17 192520 196607 2044K 0700 spare1
18 196608 229375 16.0M 0700 boot
19 229376 294911 32.0M 0700 persist
20 294912 327679 16.0M 0700 recovery
21 327680 333823 3072K 0700 modemst1
22 333824 339967 3072K 0700 modemst2
23 339968 339975 4096 0700 pad1
24 339976 346119 3072K 0700 fsg
25 346120 347143 512K 0700 fsc
26 347144 348167 512K 0700 ssd
27 348168 348175 4096 0700 pad2
28 348176 349199 512K 0700 encrypt
29 349200 350223 512K 0700 eksst
30 350224 350239 8192 0700 rct
31 350240 360447 5104K 0700 spare2
32 360448 393215 16.0M 0700 misc
33 393216 458751 32.0M 0700 laf
34 458752 524287 32.0M 0700 fota
35 524288 557055 16.0M 0700 spare3
36 557056 573439 8192K 0700 drm
37 573440 589823 8192K 0700 sns
38 589824 655359 32.0M 0700 mpt
39 655360 720895 32.0M 0700 factory
40 720896 4947967 2064M 0700 system
41 4947968 6193151 608M 0700 cache
42 6193152 6717439 256M 0700 cust
43 6717440 30736383 11.4G 0700 userdata
44 30736384 30777310 19.9M 0700 grow