We migrated from on-prem Exchange to Office 365.
Since then a handful (10-20) Executive Assistants are experiencing Outlook errors and delays when performing tasks on calendars that have been shared with them. When accepting, declining, or scheduling meetings for these calendars, Outlook hangs for 5-30 seconds on average. It frequently gives an error that they do not have access to the calendar when they try to schedule meetings and appointments from the shared calendar. These issues do not occur in OWA.
Troubleshooting so far:
Outlook profile has been rebuilt and cache cleared.
Cached mode for EA's on and off.
Download shared folders on and off.
SecureAuth is working appropriately and that it is not causing any issues related to authentication.
Physical location does not appear to be the source of the issue. We've had reports from various buildings and regions of the same issues.
Hardware is varied and the issues persisting through multiple laptop replacements indicate that this is likely not the source of the issue.
Users are on Office 365 and Outlook 2016, issues is persistent across all platforms.
Determined GPO doesn't appear to be part of the problem.