Same issue here at two customers of mine. Also tried to move the qvd files to another location and also checked if the app can access the archive log folder. Everything is fine except the task data still missing. Only reloads made in the workspace are loaded into the app, the published one's are still missing. In the qvd file the data does exist, but the Operations Monitor seems to filter it out.
I found a KBA that advises to import the default "Reloads Monitor" app from C:\ProgramData\Qlik\Sense\Repository\DefaultApps and this works for me. I can't find the related KBA anymore, but I'm sure it exists.