Participants getting removed from meeting chat despite same invitation process

Hi everyone, 

i know that participants are getting removed from meeting chat if they arent invited via calendar. We have monthly session where all the participants are invited via teams link, not the calendar. Normally this leads to the point that they are getting removed from the meeting chat after the meeting ended. Last week i had the same call and nothing changed (as far as i know), but people still had access after the meeting ended. (was possible to write sth in the chat) This is pretty weird. Does someone know under which curcumstances this fact appears? I havent found anything in this forum to this specific instance. 😕

BR Dominik