I'm not sure if this is a general problem so posting here first to get other people's status: Just now I did not get an achievement with patched mcc exe and achievement enabler trainer, tried it twice and did not work (but did all the time in the last few weeks). Tried again without cheats and EAC enabled, it popped directly. Might be an update that broke something?
[Edited by fsmcas, 3/1/2021 4:45:24 AM]
I've gotten 517/700 %73 percent complete, been working fine for me. Make sure the whole master chief folder and any trainers are in you exclusion list for your security/anti-virus software. Activate the enabler at the main menu of the game, pick a game load in then activate the corresponding trainer.
Hm, will try it when I get to any ne acievment. I've used it correctly for several playthroighs and it always worked, that's why I posted. Due to the nature of achievements I can just test it again, but I will update when I get another one.
Try using the normal launch option and not the non-eac one when the little steam window pops up.