How to force re-distribution of extensions in a multisite setup?

I have a theory… Maybe I’ve messed up with my site directory structure?
I notice that lib/check_mk is a symbolic link to lib/python3/cmk
But local/lib/check_mk is not a symbolic link to local/lib/python3/cmk. Could this be the issue?
At least all working checks reside in local/lib/pyton3/cmk whereas everything I install to local/lib/check_mk won’t work…