Potentially dangerous behaviour was detected. The request will be ignored. [810452]

Strange so you only get this error in the qer-app-operationssupport and not in qer-app-portal?
And you did perform an IISReset after the change.

I can only reproduce this error if the BaseUrl don't match up in QBMWebApplication and in the web.config (include the trailing slash / at the end just to be sure ) in both qer-app-operationssupport and qer-app-portal

BaseURL@QBMWebApplication = https://itshop.local.net/ApiServerDev/
web.config <add key="BaseUrl" value="https://itshop.local.net/ApiServerDev/" />

in System journal I see two errors:

SQL injection detected in WHERE clause: messagetype = 'E' and messagedate > DateAdd(dd, -1, GetUTCDate())

and

SQL injection detected in WHERE clause: (lastjobfetchtime < dateadd(mi, -10, getutcdate())) and (IsQBMServiceInstalled = 1)

...that does not look strange to me ... al buil

t in logic!

in System journal I see two errors:

SQL injection detected in WHERE clause: messagetype = 'E' and messagedate > DateAdd(dd, -1, GetUTCDate())

and

SQL injection detected in WHERE clause: (lastjobfetchtime < dateadd(mi, -10, getutcdate())) and (IsQBMServiceInstalled = 1)

...that does not look strange to me ... al buil

t in logic!