I tested with my friend when lopunny was switch into sticky web and speed -1 stage. After that, it mega and vs my poke with 271 speed. We found that mega lopunny became speed tie with 271 speed poke which is impossible.
Mega lopunny -1 stage should be cal as max speed 405*2/3 = 270 speed.
Hope any MOD can solve this battle bug. Have a good day!