Multi-account containers doesn't sync, and breaks overall Firefox sync

Hi all, I have another query ongoing which trying to fix seems to have caused this problem: https://support.mozilla.org/en-US/questions/1581166 I'm logged into Firefox account and have everything synced. I've logged multi-account containers (MAC) into my Firefox to try and sync accounts. However, the containers are not syncing AND I now cannot send tabs to or from this instance of Firefox. This started either after I refreshed Firefox or after I reinstalled it, I'm not sure which. Before Refresh I definitely had full sync, and I believe containers were synced but I had not changed anything in MAC for a long time, many months maybe years. To try and fix this, I logged out of my Firefox account for both MAC and the whole browser, then closed Firefox. I then restarted Firefox, logged into my Firefox account and tested that I could send and receive tabs - I could, so that worked. I then logged into my Firefox account with MAC and tried to send a tab, and I couldn't, and nor did the containers sync. So, it seems that the MAC addon breaks sync. A workaround is just to not depend on containers sync, but I'd prefer to get this back. Any suggestions on how to fix this, or is this a bug in Firefox or MAC? Cheers :)