The cause of this problem can be found by debugging the script, just like in any other QlikView document.
Script line error:
Let duration_min = ceil((peek('SessionTimeStamp',0,0'tmp_incrementalConcurrency')-42471.418344907)/-/60/24)
Apparently, variable sessStart is undefined, resulting in a single minus sign between two slashes. That's an illegal expression in QlikView script.
The error location is line 29 in (hidden) script tab SessionConcurrency.
The line where sessStart is (not) set is line 28.
As I don't have your environment at my disposal, I cannot replay what is happening during a reload at your place.
I know this has been marked resolved, but are you still seeing this?
I am curious if you saw this initially when reloading via QMC (Publisher)?
It is related to the field "Session Concurrency Interval" which is set to "Always one selected value" but is sometimes unselected somehow when the app is reloaded in QMC.
The way to check is to look at the app in Access Point after it reloaded and check the "Session Concurrency Interval" value selected on the Configuration page. (You might need to "Always show" the configuration page by clicking that setting on the "Scan Details" page of the app.). If there is no Session Concurrency Interval value selected, then you have encountered this issue.
Please let us know if you see this behavior!