Azure DevOps for Jira (Official) currently only uses Webhooks to get information from Azure to Jira. This means it only brings information from the time when it is configured successfully on, and if there are any issues with the connection for any reason, there is no way to sync older/missing information, as mentioned on JRACLOUD-87205 - Provide backfill option for Azure DevOps for Jira (Official).

There is also no available logging or warnings in case the webhooks fail for any reason. With that, it is possible the connection fails for many days before someone notices, and anything from the time the failure started until the failure is fixed simply won't be synced to Jira.
In any case, not noticing the problem and not being able to determine when the problem started may cause significant risks in managing releases.

The suggestion here, therefore, would be to implement some kind of notification and/or logging so that the users would be able to check/be warned if the connection is failing and confirm when exactly the problem started. That will also make it easier to understand which specific data will be missing in Jira and can't be recovered.