Can't connect to Realms - Xbox One S

Since the "Better Together" update have had an issue where my sons can't connect to Realms through their Xbox Live accounts on their Xbox One S. Sometimes they can - but I would say that at least 8 out of 10 attempts they can't. Normally I need to go in and take them off the Realm and readd them and they can connect at that stage - but then the next time they try they can't again.

However they can connect using their laptop/android tablets every time they attempt to.

Can you please confirm.

Thanks