I found it when using libloot v.0.15.1 with Skyrim Special Edition. The following load order is used:

[...]
HearthFires.esm
[...]
AyleidCitadel.esp
[...]

Both files, of course, exist with the name matching the above.

AyleidCitadel.esp contains Hearthfires.esm as master (note the lower case f) which causes loading of the plugin to fail (missing master) on Linux.

Even on Linux with the string comparison being case-sensitive, the names in the TES4 record should be compared case-insensitively when trying to find the corresponding master.

The corresponding mod can be found here: https://www.nexusmods.com/skyrimspecialedition/mods/11307