[Xperia Z3 Q&A, Help & Troubleshooting] hcwdjk:
So I just got a new Z3 D6603. It's running on stock Marshmallow, 23.5.A.0.570. Bootloader was never unlocked, it has never been rooted.

Everything is running fine, except there's a constant screen stutter in literally everything: regular apps, videos, gaming, everywhere.

I've made an app that shows this nicely. I'm attaching the apk. It simply draws a line that should smoothly move across the screen. It does move smoothly on all phones I've tried it on, except my Z3. Here's a video I made that shows this app running on a 1st gen Moto G (left) and the Z3: https://www.youtube.com/watch?v=Wqgr9u_4Sa0&feature=youtu.be. Unfortunately this video adds some stuttering on it's own, but in a few places you can still clearly see the problem, especially near the end of the video.

I've looked into the logs and every time there's a stutter, a bunch of these show up:

05-01 21:02:07.877 6699 6699 W osmcore : type=1400 audit(0.0:3470533): avc: denied { getattr } for path="/proc/1" dev="proc" ino=935969 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:07.877 6699 6699 W osmcore : type=1400 audit(0.0:3470534): avc: denied { getattr } for path="/proc/2" dev="proc" ino=935970 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:07.877 6699 6699 W osmcore : type=1400 audit(0.0:3470535): avc: denied { getattr } for path="/proc/3" dev="proc" ino=935971 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:07.877 6699 6699 W osmcore : type=1400 audit(0.0:3470536): avc: denied { getattr } for path="/proc/6" dev="proc" ino=935972 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:07.877 6699 6699 W osmcore : type=1400 audit(0.0:3470537): avc: denied { getattr } for path="/proc/7" dev="proc" ino=935973 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:09.987 6699 6699 W osmcore : type=1400 audit(0.0:3470793): avc: denied { getattr } for path="/proc/1" dev="proc" ino=935969 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:09.987 6699 6699 W osmcore : type=1400 audit(0.0:3470794): avc: denied { getattr } for path="/proc/2" dev="proc" ino=935970 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:09.987 6699 6699 W osmcore : type=1400 audit(0.0:3470795): avc: denied { getattr } for path="/proc/3" dev="proc" ino=935971 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:09.987 6699 6699 W osmcore : type=1400 audit(0.0:3470796): avc: denied { getattr } for path="/proc/6" dev="proc" ino=935972 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"
05-01 21:02:09.987 6699 6699 W osmcore : type=1400 audit(0.0:3470797): avc: denied { getattr } for path="/proc/7" dev="proc" ino=935973 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:kernel:s0 tclass=dir permissive=0 ppid=1 pcomm="init" tgid=1 tgcomm="init"

Any help is welcome. Especially, if you have a stock ROM on your Z3, can you please

a) install the attached apk and see if you can spot the stuttering

b) look into the logs and see if you have those messages from osmcore popping up every few seconds?

Thanks in advance.

EDIT: found the problem myself: it was somehow caused by OS Monitor: https://play.google.com/store/apps/details?id=com.eolwral.osmonitor&hl=en. The problem went away after killing this app.