We have a scheduled flow that has a Messaging Notification core action followed by an update to the Messaging Session and an update to the Messaging User, in that order.
The notification is received but while Updating the Messaging User we have this error
After tests it seems that if we remove the Messaging Notification core action the Update proceeds with no issues.
I don't see anything on the documentation about automatic updates to the Messaging User after the notification is send that may cause the lock error.
Any Idea on why is the Messaging User record locked in this case?
Bradley Weller (Fast Slow Motion) 
Forum Ambassador
The Messaging Notification Core Action has strange behavior. It can be placed in the middle of a Flow and the creation of the Messaging Sessions seems to happen in the appropriate sequence. However, from my previous observation, the actual Messaging Notification does not happen until the rest of the Flow resolves so right after/as you are updating the Messaging User. It seems that the Messaging Notification locks the Messaging User up until the Flow completes.
