iMessage not working with certain MacBook contacts

I use Mac for work. We're a small company of about 20 employees and I only use messages to talk to them, never anyone else. I also only use this one device- MacBook Pro 2017. I few weeks ago I was randomly blocked from iMessage but I managed to sort this quickly with apple support. Now however, some members of my company cannot see me in group chats. They can message me, but my messages direct to them show as not delivered. Everyone else can talk to me as normal and see me in group chats. So far I know of five people who can see me and three who can't. Unfortunately one of the people who can't is the boss, which is causing significant inconvenience as I can't inform him of my submitted work as I'm supposed to.

I have used the apple support chat several times and made two phone calls. A very kind technician even shared my screen and walked me through everything she can think of, but she could not diagnose the problem. There is absolutely nothing wrong with my settings or account.

I got one of the people who can't see me to restart her Mac but that didn't fix the problem. I have obviously restarted my own Mac as well, as well as all the things like updating and so on that the support team will recommend to you.

As a last ditch effort I'm putting it out to the community in case anyone else has had a similar problem and fixed it. There's no pattern as to who can and can't see me.