I was able to comment in these threads from my PC via the Alexandrite frontend, but attempting to view those comments via Sync displays "Could not load post" with an option to Retry, which does not succeed.
Post 1 appears visible when opening the community, but opening the post displays the same error. Post 2 (the sh.itjust.works link which is posted on a lemmy.world community) the post does not appear in the community at all in Sync.
Confirmed that these communities/users are not blocked on my account, and no filters set within the app should apply to these posts either.