A retention policy is configured in Managed Folder Assistant (MFA) to archive old messages from Exchange On-Premises mailboxes to Exchange Online. However, files that are larger than 35 MB are not moved.
To fix this issue, install Cumulative Update 13 or a later cumulative update for Exchange Server 2019.
The new default value for the retention policy is 150 MB.
To increase the default maximum file size for archived files, run the following override.
Note In this command, replace "XXX" with the new file size in MB.
New-SettingOverride -Name "MaxMessageMoveSizeInMB" -Component ElcAssistant -Section ElcRemoteArchiveSettings -Parameters @("MaxMessageMoveSizeInMB=XXX") -Reason "Size Increase"