In your stack trace I see the following:
Transaction (Process ID 136) was deadlocked on lock | communication buffer resources with another process and has been chosen as the deadlock victim. Rerun the transaction.
This means that a deadlock is causing your error. It looks like in 8.18.0 Mendix already made some changes to reduce the chance of deadlocks, but that doesn't make them impossible.
This forum question is a good resource on how to prevent deadlocks:
https://forum.mendix.com/link/space/app-development/questions/3612