Yeah sounds like a block of some kind on the client itself. Can you start then from browser client and or mobile device? Another pc? Sign out and in fixed many things with desktop client. Try those things and report back and we can go from there.
I removed my previous comment because I rushed through reading this and it can't possibly be the Meet Now settings in the S&T admin centre because Meet Now feature is available. Sorry about that - it is obviously in the direction you guys are heading with the either SfB or a block on the local machine.