Honestly I started using obtainium because I can't figure out why F-Ddoid builds are a month behind. RedReader became completely broken and needed the newer version. Not sure what's up with that lag. It's extremely frustrating.
Anyhow, when the apps stop being updated, it's usually due to something that was added that doesn't make them compliant with F-Droid's policies anymore; or, they changed something in the release process without telling F-Droid.
Other times, the apps were set to be updated only at the developer's request, and for some reason they still haven't done that request (some developers deliberately update F-Droid less frequently, to be more confident of not giving bugged releases to the F-Droid usere).
The normal delay, due to their manual (and lazy) signing process, is from few days to about ten
