If you have updated your instance to Peertube 6.1.0, and if you use the livechat plugin (any version above 6.3.0, and previous to 9.0.2), the federation is broken: your server won’t be able to send any video update.
This is due to new data validation in Peertube v6.1.0, and insufficient data type declaration in the plugin.
This affects all videos, even video without chat, and non-live videos.
This is fixed in livechat v9.0.2, that i just published. You should update as soon as possible.
It can take up to 12 or 24h for this version to be available on your instance. If it is not available, just uninstall the plugin, and wait (or run update "plugin" set "latestVersion" = '9.0.2' where "name" = 'livechat'; in your postgresql database, then go to the plugin list to upgrade).
Really sorry for the inconvenience. I did not see the bug when the 6.1.0-RC1 was released.