I recently had the problem that content wasn't federated too at https://veganbtw.net/c/veg_discussion and https://feddit.de/c/veg_discussion@veganbtw.net.
In the past there was a similar issue where one instance had too few workers allocated to "pushing" the changes to other instances, so maybe an instance specific problem?
EDIT: maybe also just overloaded because of the new members from the kuketzblog community?