Dh is currently having a similar issue at work. It's an informal Facebook group chat, he wasn't keen on being added to the chat to start with, he doesn't really use social media and likes to not have to be checking his phone when he's trying to unwind.
For the first month or so it was mostly social type stuff and because he didn't really want to be in there because it's a stressful job at the best of times and he wanted to keep work/home separate so he just put it on mute and checked in every couple of days or so. Until a month ago, his manager gave him shit for being "late" for work when he wasn't, she'd put a general "people on shift b, start at 8 am tomorrow instead of 11" and he, and a couple of others didn't see it.
She says if people won't use the chat than it's their own fault they don't know their hours have been changed or changes to location. She says it makes her job easier this way, but that's the thing, it's her job and she gets paid for her time dh and his colleagues are not and it's low paid stressful job with daily abuse from clients, they need to unwind and she doesn't seem to understand that her "takes two seconds to check" is more than that for some staff because it stops them from relaxing at home. It's almost like being on call without the on call wage.
My brother started a new job at Xmas and declined being added to a "casual" work group chat and his boss basically told him it makes his chances of being kept on at the end of his probation period less because they like people who are flexible, go the extra mile and are a team player, he changed jobs and the unwritten expectation to not only be in group chat but to actually read the messages and engage daily was part of the reason because his wife, rightly, expected him to be present and engaging with his kids instead of being on his phone discussing agendas for x meeting and not being paid for that time.