Steam reports no errors but cannot boot into GUI.

[WiseKind]

Hello. I posted a thread about a similar problem to this one, and found that the solution was to install some packages according to a guide on the Internet. It turns out that Steam working after that was merely a coincidence. I am now randomly experiencing the problem, and I am yet again lost. Steam does not report any errors, nor does any other application on my computer when launching Steam, it just boots up to the login manager and immediately quits prematurely. I cannot play my games until I find out what is causing Steam to quit.

Running Steam on arch rolling 64-bit
STEAM_RUNTIME is enabled automatically
Pins up-to-date!
Steam client's requirements are satisfied
/home/lonefox256/.local/share/Steam/ubuntu12_32/steam
[2020-12-03 13:53:16] Startup - updater built Dec  2 2020 00:26:37
[2020-12-03 13:53:17] Opted in to client beta 'publicbeta' via beta file
You are in the 'publicbeta' client beta.
Installing breakpad exception handler for appid(steam)/version(1606876649)
[2020-12-03 13:53:19] Loading cached metrics from disk (/home/lonefox256/.local/share/Steam/package/steam_client_metrics.bin)
[2020-12-03 13:53:19] Using the following download hosts for Public, Realm steamglobal
[2020-12-03 13:53:19] 1. http://media4.steampowered.com, /client/, Realm 'steamglobal', weight was 100, source = 'update_hosts_cached.vdf'
Installing breakpad exception handler for appid(steam)/version(1606876649)
[2020-12-03 13:53:19] Verifying installation...
[2020-12-03 13:53:20] Verification complete
Loaded SDL version 2.0.13-6234804
Installing breakpad exception handler for appid(steam)/version(1606876649)
STEAM_RUNTIME_HEAVY: ./steam-runtime-heavy
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
CAppInfoCacheReadFromDiskThread took 250 milliseconds to initialize
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
[1203/135332.016470:INFO:crash_reporting.cc(247)] Crash reporting enabled for process: browser
[1203/135332.857552:WARNING:crash_reporting.cc(286)] Failed to set crash key: UserID with value: 0
[1203/135332.857635:WARNING:crash_reporting.cc(286)] Failed to set crash key: BuildID with value: 1606868822
[1203/135332.857640:WARNING:crash_reporting.cc(286)] Failed to set crash key: SteamUniverse with value: Public
[1203/135332.857645:WARNING:crash_reporting.cc(286)] Failed to set crash key: Vendor with value: Valve
CApplicationManagerPopulateThread took 6993 milliseconds to initialize (will have waited on CAppInfoCacheReadFromDiskThread)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Installing breakpad exception handler for appid(steam)/version(1606876649)
Proceed to auto login
No cached credentials
[1203/135338.908108:WARNING:crash_reporting.cc(286)] Failed to set crash key: UserID with value: 0
[1203/135338.908352:WARNING:crash_reporting.cc(286)] Failed to set crash key: BuildID with value: 1606868822
[1203/135338.908389:WARNING:crash_reporting.cc(286)] Failed to set crash key: SteamUniverse with value: Public
[1203/135338.908412:WARNING:crash_reporting.cc(286)] Failed to set crash key: Vendor with value: Valve
[1203/135338.910722:INFO:crash_reporting.cc(247)] Crash reporting enabled for process: gpu-process
[1203/135339.858744:ERROR:sandbox_linux.cc(372)] InitializeSandbox() called with multiple threads in process gpu-process.
[1203/135341.532444:WARNING:crash_reporting.cc(286)] Failed to set crash key: UserID with value: 0
[1203/135341.532522:WARNING:crash_reporting.cc(286)] Failed to set crash key: BuildID with value: 1606868822
[1203/135341.532528:WARNING:crash_reporting.cc(286)] Failed to set crash key: SteamUniverse with value: Public
[1203/135341.532532:WARNING:crash_reporting.cc(286)] Failed to set crash key: Vendor with value: Valve
[1203/135341.559677:INFO:crash_reporting.cc(247)] Crash reporting enabled for process: utility
INTEL-MESA: warning: Performance support disabled, consider sysctl dev.i915.perf_stream_paranoid=0

Exiting workitem thread
[2020-12-03 13:53:46] Shutdown

 

[WiseKind]

Ok, so after screwing around with random things in an unhealthy panic (The last thing I tried doing was reinstalling Gamemode, a program I use with my Steam games), I got Steam to boot up into a UI, but this problem is NOT solved. This has happened before, and it will inevitably happen again, so this thread is dedicated to finding out why this same problem happened twice, and why it's so inconsistent.

 

[WiseKind]

Idk if commenting this much is against the rules, but I think I know a plausible solution: Gamemode may be the problem.
The previous time I had Steam break, I noticed that Steam fixed itself whenever I reinstalled packages in the Chris Titus Tech Ultimate Linux Gaming Guide, and the last section of that covered gamemode. The second time, I ran through it again, but skipped the Gamemode part. However, when I tried properly uninstalling and then reinstalling Gamemode, Steam worked. I have installed Gamemode exactly the way Chris showed, without using a package manager, using this script:

git clone https://github.com/FeralInteractive/gamemode.git
cd gamemode
git checkout 1.5.1 # omit to build the master branch
./bootstrap.sh

And it seems that the reason Steam has broken multiple times is because Gamemode devs may have released an update that I didn't get automatically, which broke some gaming programs including Steam.
I noticed that Gamemode actually has a repo package for Arch, so I could install that, ditch the script so Gamemode can update automatically with the rest of my system.
Should I just mark this thread as solved? I don't know for completely sure that this is why, because when I run games with Lutris I had gotten an error with libgamemodeauto.so.0 saying that I had the wrong ELF class or something (I don't have the ability right now to replicate this log because now it's a different issue with Lutris.)
even when Steam worked fine.
Idk if I could be breaking the rules right now. I created a thread for a problem that I already had once but was prematurely marked solved, I posted a lot on this new thread (which I'm pretty sure gives me credits which I still don't know what they're used for), and now I'm pretty sure I should just mark this thread as solved, which would make this thread pointless because I didn't need help, because it's likely that Gamemode not being up-to-date is the problem. https://linux.org/help/terms/ isn't very clear on if any of those things are not allowed.