TL;DR: MC Launcher defaults to max 4GB of RAM. I change it to 10GB. Whenever the launcher closes, it resets to 4GB.
I always allocate at least 10GB of RAM to my game to ensure it runs smoothly. After setting up my initial installation I went into the launcher settings for this build and changed the max RAM allocation from 4GB to 10GB.
On my next play through, my game crashed when attempting to launch. It seemed like it was choking on the resources. I went to go check my allocations again, and sure enough, it was back at the default 4GB. This has happened each and every time I've started the launcher. The allocation I give seems to stick as long as the launcher is active. But if I have to close it for any reason and reopen it, I have to reallocate the RAM again or my game will crash.