There are quite a number of recordings where the exact recording date is not known resp. not documented. Or in other cases it is just not tagged / provided by the metadata source.
In Roon 1.7, the following logic was applied when sorting Albums by Recording Date:
When recording date is filled, use that, if not, use “Original Release Date”, if that is empty, use “Release date”. That was making a lot of sense as albums where meaningfully sorted with release date as approximation for recording date.
In Roon 1.8 that logic has gone missing / is broken. Any Albums not having Recording Date in the Tags get just dumped to the bottom of the list.
If required I can add a screen print but I guess this can easily be reproduced.
Many thanks for investigating & fixing.