so apparently they removed that ''irregular activity'' error message because on August 7 they will bring it back, this time they will detect people who log in using emulators, modded apk and ban them all, be careful after August 7 guys, don't use your main accounts after that update.
you can use it anywhere that doesn't have ranking, for example don't use it in arena, solo raid, union raid, tribe towers, story mode, you can use it freely in simulation room, lost sector, interception, event challenge, event story stages.