MC Launcher newest version isnt saving custom jvm, screen parameters in profile data.
After every launcher restart, the data gets set back.

-> profiles are not for vanilla mc, they are for forge modpacks.

My settings:

-Xmx12g -Xms8g -XX:PermSize=2g -Dminecraft.applet.TargetDirectory="E:\minecraft\Instances\Minecraft Time" -Dfml.ignorePatchDiscrepancies=true -Dfml.ignoreInvalidMinecraftCertificates=true -Duser.language=en -Duser.country=CH

gets resetet after a restart::

-Xmx3072m -Xms256m -XX:PermSize=256m -Dminecraft.applet.TargetDirectory="E:\minecraft\Instances\Minecraft Time" -Dfml.ignorePatchDiscrepancies=true -Dfml.ignoreInvalidMinecraftCertificates=true -Duser.language=en -Duser.country=US

Also for screen resolution: gets back to 1024x768.

--> would also be neat to define standard values on our own, so every profile takes Xmx, Xms from another source.

EDIT::: SOLVE::

it's the new twitch launcher.. just go in twitch to settings -> minecraft change it there and the launcher from mc will get the data from there.