Local repository does not contain modular metadata


I have been running a local repository (mostly using DNF local; after the upgrade I just copied all the cached RPMs from system-upgrade) to keep a bunch of offline computers up-to-date. After I updated to Fedora 31, the offline computers (well, so far the only one I’ve been using for testing) fail with
No available modular metadata for modular package 'XXX', it cannot be installed on the system
Is there anything else that I need to do besides running createrepo_c?
I assume that the information I need is hidden somewhere in here:

Can someone point me in the right direction, please? :slight_smile: I need to make the whole update process as automatic and easy as possible.
Thanks beforehand!

Creating modular repositories is detailed here:

It seems that only a few packages were problematic. There are other modular packages and they can be installed OK without any extra hassle. Thanks for chipping in though!