Currently Qt Assistant will cache qhc file, for things like providing Bookmarks support. Such approach often just works but it also often doesn't work and the only solution is to delete the cached .qhc file manually. Looking for reference on the internet, this has been discussed for around a decade now, on different help forums. Solution being to (manually) delete the cached .qhc file. In FreeCAD we would like to provide help files included in an AppImage format. I shared some details here:

https://bugreports.qt.io/browse/QTBUG-12050

AppImage works in a way it always changes its runtime location, on each AppImage start. Help will therefore work only on the first run, on the second run it will fail to work, due to cached  qhc file getting involved. I tired to programmatically unregistered and register the help files, at each AppImage start, but it fails and Qt Assistant doesn't provider a reason  why. In addition i wanted to add support for picking up help files from two locations, one located in home folder and one in system wide location. For such use case cached qhc file will start to cause issues again. As if the help files are first found in home folder and at any time somebody decided to use the system provided help files, removing the ones from home folder will left the cached qhc file intact. The system provided help files will again fail to work correctly, until manually deleting the  cached qhc file.

In short, it would be nice to have an option to opt-out of qhc cache usage.