My instance (frozeninferno.xyz) seems not to be federating properly with mander.xyz.

Looking at https://lemmy.frozeninferno.xyz/c/[email protected] it appears that the newest posts are from 4 months ago, however, looking at https://mander.xyz/c/herpetology there have been some more recent than that.

What can I do to fix this? And how can I check if federation is working properly with other instances?

Thanks.