The warnings on the load seem to come from an issue with the monitoring setup. I've seen this before, the app has multiple processors let's say 4 then the max load would be 4.0. The monitoring however still thinks the app has 1 processor so a load of 0.97 will trigger the notification. Correlating the actions to the CPU load is not an easy task and does not really seem necessary with the current load. The max load on the app is 0.97/4.0 *100 = 24.25%. I would file a ticket with support to fix the notification settings.
When we upgraded our app from Mendix 5.16.1 to 5.19.0 we experienced exactly the same:
We now also receive a lot of CPU alerts for our environment that we just ignore (because they'll automatically be "fixed" within a few minutes).
Seeing that you have the exact same symptoms, I think something was changed in Mendix 5.17/5.18/5.19 that caused this.