Exchange Online users cannot see on premises users free/busy time information- July 2019
One of my clients has a hybrid environment configured with Exchange 2010 and Exchange Online. Out of nowhere, migrated Office 365/ Exchange Online users could not see on premises user or conference room calendars. I checked and luckily enough there was an advisory out for this with a possible resolution.
Turns out Microsoft updated an SSL Certificate on the Federation gateway that is used by hybrid environments.
In order to correct this you have to run the following command-
Using the Exchange PowerShell module- _Get-Federationtrust | Set-FederationTrust –RefreshMetadata_
This will correct the issue but you'll also need to create a scheduled task to make sure the metadata refresh continues to happen.
Schtasks /create /sc Daily /tn FedRefresh /tr “C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe -version 2.0 -command Add-PSSnapIn Microsoft.Exchange.Management.PowerShell.E2010;$fedTrust = Get-FederationTrust;Set-FederationTrust -Identity $fedTrust.Name -RefreshMetadata” /ru System