UPnP on iOS with Kodi Server - Some folders not listing media

Steps to reproduce Connect to a Kodi UPnP server. Go to Music Library -> Artists -> [Artist name] -> [Album name] or Video Library -> TV shows -> Title -> [TV Show name] -> Season [number]

Expected results A listing of media items (e.g. songs in an album)

Actual results Throbber keeps spinning, no error message produced.

Description In VLC for iOS Version 3.2.13 (375) I connect to a Kodi UPnP server (Kodi version 17.6) running on Ubuntu 18.04.

The server appears as it should, and I can browse folders, but certain folders are not loading. The throbber just keeps spinning, but no error message is ever produced.

Folders that doesn't work are music albums (Music Library -> Artists -> [Artist name] -> [Album name]) and listings of episodes in a TV series season (Video Library -> TV shows -> Title -> [TV Show name] -> Season [number]). I can list and play albums when I find them directly via the 'Albums' listing, where all albums are listed, and all media items can be found, when looking under the 'Files', but those methods are impractical.

Occasionally the root folder of the UPnP servers is also not loading, but I am not sure if that is a separate issue? I can connect to the same server over SMB with no problems.

Testing on VLC for Android (3.3.4) shows no issues with the same folders on the same server, same WIFI etc..