• Minecraft Version: 1.12.2
• BetterFps Version: 1.4.8
• Forge/LiteLoader Version (if any): 14.23.2.2619
• Crash Logs (if any): no crashreport
• Other Mods (if any): OptiFine_1.12.2_HD_U_D1

BetterFPS and OptFine are not doing well together. If both mods are in the pack, java gets a problem and needs to quit.

Try updating forge to the latest or recommended version

I have a similar issue. It was working fine until I added Optifine to the mods folder. Then this started happening:

Note: It's flashing

EDIT: Nevermind, it's not your fault. Persists without BetterFPS — stops when resize the window?