In this case, it's one specific channel: https://diode.zone/c/andybalaam_lectures/videos?s=1. That is, !andybalaam_lectures@diode.zone. It's run by @andybalaam@lemmy.ml / @andybalaam@mastodon.social

AFAICT, federation hasn't been working from this channel to lemmy for ~3 months, for all the instances I checked (perhaps a particular lemmy version broke things?).

EG:

• the view on lemmy.ml
• on lemm.ee
• on programming.dev
• and on endlesstalk.org

By comparison:

• mastodon.social is up-to-date: https://mastodon.social/@andybalaam_lectures@diode.zone
• And on hachyderm.io, following the user (rather than the channel) is also up-to-date: https://hachyderm.io/deck/@andybalaam@diode.zone

I'm not following anything else on peertube so I don't know how common this is (and I couldn't find anything on the GitHub issues), but different behaviour on mastodon and lemmy would superficially indicate that it's a lemmy problem, which would be a shame given that lemmy is much better for consuming peertube.