iMessage not syncing immediately from iPhone to MacBook

iMessage NOT syncing immediately from iPhone to MacBook when both have working wifi

This is a recent occurrence and up until a couple of weeks ago has been working for years.

I have rebooted both devices. I have signed in and out of iMessage.

Messages sent via iPhone on iMessage do not show up for days afterwards sometimes on the MacBook - even if I send myself a message to try and get the other chats to refresh/update/sync

If I send a message in the problematic chat then it does sync but I don't want to do that as that's annoying for the other person plus it might be out of context as a reply.