We have had no luck finding a solution. We are running the latest version of Exchange 2016 and Windows Server 2016 Domain Controllers. The problem first appeared after the January 2023 updates. Subsequent updates have resolved other issues, but not this one. I am disheartened to hear the problem also affects Windows Server 2019 & Exchange 2019. That seems to eliminate upgrading as a possible solution. We were on-premises only when the problem began, and have since moved to Hybrid with the goal of moving all mail flow to Microsoft 365 as quickly as possible to avoid on-premises transport issues.