Use the console, try simply typing this into it before entering the region:
@Trigger(REGION_ENTER_AND_STOP_TRIGGER,"reg_1",nil);
and check if the trigger activates. Perhaps some error will appear, for example, due to a typo.

Thank you very much for the advice. Strangely, neither the console nor the HOMM5 script editor reported any errors, but the reset didn't work. I placed sleep(5) after the question box and then the reset, and it started working, although I don't understand why sleep was needed there...

And one more question. How can I create a function that checks whether a player has visited a region? I don't want to write 5 different quests for 5 regions and do everything through REGION_ENTER_AND_STOP_TRIGGER. I would like to do everything through one quest... Thank you very much in advance.