Check this out: https://join-lemmy.org/docs/administration/troubleshooting.html#you-dont-receive-actions-reliably
(However, afaik your instance must receive activity so that said activity can be federated to other instances. That's why you can comment on dead instance comms, but they never will be seen on other instances. Take lemm.ee for example.)
Also, as davel said, the instances page seems to be broken, and that doesn't seem to be a frontend issue as not even lemmy federation state checker is able to query it, so either something is wrong at the backend or your reverse proxy config.
Check the logs and config.
edit: wrong, ignore.