using mod form latest action and other mods
["UniversalTweaks-1.12.2-1.11.0.jar"
"!configanytime-3.0.jar"
"!mixinbooter-9.1.jar"*not related just forgot to delete
"CustomMainMenu-MC1.12.2-2.0.9.1.jar"
"FpsReducer-mc1.12.2-1.20.jar"
"ResourceLoader-MC1.12.1-1.5.3.jar"]
are latest version
using nomiceu1.7a4 resources

And you're confident that the issue is solely caused by Universal Tweaks? If so, please try to determine the related config setting.

it happened when mainmenu fps limited by fpsreducer or other mods/manually set below 20fps
caused by

     # Removes the hardcoded 30 FPS limit in screens like the main menu
    B:"Uncap FPS"=true

all loaded mods:

Well, when other mods are affecting the FPS of the main menu, you simply have to disable the tweak as they are essentially modifying the same thing.