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.
PalletJacker
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.