I have the same issue and have somehow a workaround.
The message box is kept showing because after clicking “OK” on the message box the “mouspointer” is jumping back to the field by entering it and than starting the microflow again.
To solve this, I just added “show a page” action to my microflow. So the page is reloading and the “mouspointer” is not jumping to the field again.
I reproduced this in 7.22.2 and i’m 99 percent sure its a bug. I would log a ticket with mendix support. This occurred with a microflow and show page as the on enter event. Would an on change or on leave event work? If not, you can also try the bootstrap tool tip widget.
bootstrap tool tip
Link to support