minecraft java launcher keeps resetting installation profile settings (ie. ram/directory)

that's a launcher issue

I too am having this issue with the game directory and JVM arguments resetting on several systems, and it is sporadic. Based on several recommendations online I am using these JVM arguments:

-Xms6G -Xmx6G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=https://mcflags.emc.gs -Daikars.new.flags=true

The "game output" windows shows that I'm running java version 1.8.0_51 from the Minecraft Launcher\runtime\jre-legacy\windows-x64\jre-legacy directory.

It doesn't do it every time, however it is happening on 5 different systems. Surely someone else has experienced this or can offer some suggestions to help narrow down the problem? I am willing to provide any information or troubleshooting necessary to resolve this issue. Whatever you need to know, just ask.

My game is modded (running Forge 36.1.0) but the mods should have no effect on the game launcher whatsoever, since the launcher settings are loaded and saved before any modded files are used.

Also, I can confirm that the JVM arguments work

Likely duplicates MCL-14797

I'm also having the exact same bug - it makes it impossible to manage multiple minecraft versions in different directories.

My solution to this problem was to just use MultiMC. It's incredible just how much better MultiMC is, especially if you do anything with mods. You can have multiple instances that work completely independently of each other and you never have to worry about all of the stuff that the default launcher randomly breaks on it's own. You can disable automatic updates on MultiMC and have a completely static, non-changing Minecraft configuration.

I set up a private Forge server (with mods, a custom resource pack, etc.) for several friends and I was able to give them my MultiMC installation completely pre-configured. All they had to do was unzip it, run it, log in to their own Minecraft account and it just works 100% of the time with no tinkering required ever. It doesn't even require installation. It is a 100% portable application. This is what Minecraft Java edition should be in 2021. With the default launcher I had to help people constantly fix the settings that would randomly get broken or would simply not save properly, and the process of having multiple versions installed at once is very convoluted.

I noticed this happening while adding mods;  A new batch of mods I had installed was causing issues (hanging) so I removed them all and started adding them back individually.  Each time I added a mod, and restarted the game, the JVM arguments had reverted to default.  I cycled through a few more mods and found that after a new mod was added to the mods folder, the next time I opened the launcher, the JVM arguments had returned to default before running the game.