Hi,
We have a AP 450i with 10 SMs registered, and this SM's were dropped suddenly staying offline for two hours. Verifying the event log we didn't have any event about loss off sync.
What can be the cause?
Without additional information, it would be tough to even guess what the problem might be.
I would suggest opening a support ticket, as they are trained to gather the proper information to help come to a diagnosis of the issue.
Go to the Cambium Support Portal and click the "Submit a Request" button at the top of the page.