I had similar issues. I'm 99% sure it was something wrong with the phone radio that was all the time attempting to connect to LTE (where my chip is capped to 3G only) so my fix was to only allow 3G and 2G.
However I also did other things before that that might have also helped:
- On location services, disable wifi and bluetooth optimizations/improvements
- Sweep through all settings (I can't remember exactly where they were) and disable everything related to auto reporting such as sending reports to google and samsung, and automatic system scans, there's a lot of hidden garbage like that, just make sure you go through all settings and disable as much as you can
- On another desperate attempt I purchased package disable pro, and disabled lots of stuff, I don't if it helped or not, but at least there are less background services running.
- Look for any apps that might also do too much work in background, the best test is to unplug your phone at 100% at night and after ~8hs of sleep and completely no use (not even moving the device around so doze can work) take a look in the moring at the battery usage, you shouldn't really have many things there, only phone idle, phone radio, android OS and android system, and probably a tiny bit of screen and google services, but really nothing else. Make sure you do this with either plane mode or all internet disabled so you don't get notifications (and you will sleep better!)