Hybrid Free Busy Issue

[neilhiorns]

We are using Exchange 2016 CU20 and have setup hybrid connection to Exchange Online using the HCW and for our central site all is working well. However, we have some Exchange servers in other countries and they are unable to see the Free / Busy information for 365 mailboxes, but the 365 mailboxes can see their FB info. As mentioned this is only occurring for mailboxes in the non central site (which have the connectors to 365).

Any hints on where to look to resolve this issue?

[#2]

It can be several things but I usually recommend reading these articles first to make sure you have a supported design:
https://techcommunity.microsoft.com/t5/exchange-team-blog/the-hybrid-mesh/ba-p/605910
and
https://techcommunity.microsoft.com/t5/exchange-team-blog/demystifying-hybrid-free-busy-what-are-the...
and
https://techcommunity.microsoft.com/t5/exchange-team-blog/demystifying-hybrid-free-busy-finding-erro...

I recommend running the tests on this website as it will often give you a helpful error message to research:
https://testconnectivity.microsoft.com/tests/o365

This article has saved me several times.
https://docs.microsoft.com/en-US/exchange/troubleshoot/calendars/cannot-view-freebusy-information-fo...

Once I had to refresh the metadata with this command:
Get-FederationTrust | Set-FederationTrust -RefreshMetadata

These commands are helpful to run in the on-premises Exchange Management Shell:
Test-FederationTrust and Test-OrganizationRelationship
See what error messages you get.