Calendar list empty

[Forage]

ICSx5 2.0.2
Android 12 (LineageOS+microg)
OnePlus 6

When adding a calendar from webcal.guru by URL the calendar gets added, but the list on the main "My Subscriptions" window remains empty.

I know it gets added because the calendar and events are visible in the Android calendar app.

What could be the cause?

[Forage]

It looks like the issue is related to first use.
If I add the first calendar after installing the app the list remains empty. If I force close the app and open it again the subscriptions are visible and new added ones after that as well.