Sorry, something went wrong

I'm having this issue on a d9 site as well as having the same issue on a site running d7 and version 7.x-2.3

When logged out the page plugin displays properly.

When logged in there's something causing it to fail and display a message in the iframe along with the cover photo (so I know it's working to spme extent): "Sorry, something went wrong". In the inspector I see this message on both sites and so far I haven't been able to track down why. I got report of it happening first a couple of weeks ago (or so) but it seemed to go away without me doing anything,.. but now it seems to be persistent. Here is the error I'm seeing:

ErrorUtils caught an error:

Found null hrp, blocking mods: ExceptionDialog; non-blocking mods: ; response error: 1357032, summary: Something went wrong, description: Please try refreshing the Page or closing and reopening your browser window.

Subsequent non-fatal errors won't be logged; see https://fburl.com/debugjs.
errorListener @ 5Abo1NGnxwm.js?_nc_x=Ij3Wp8lg5Kz:58

I've tried clearing the cache, turning off js aggregation in Performance settings. I know the connection settings are correct, and I've checked at facebook developer portal to see if there was something there that helped me.... and I've looked here of course. It's always possible I've missed something but I haven't found it yet.

Any help appreciated.