Shared mailbox disappearing

I have two users that share the same shared mailbox O365. They have their own personal email but share our customer service mailbox. When you open outlook 2019 (that's up to date) the shared mail box shows. bottom right status says updating share folder. Then it just disappears. If I login to outlook with just that share account it works fine. What I think it started when the main user password changed, then I think the problem started with the shared. Both users don't recall when it started disappearing.