Cool - thanks for sharing that snippet. I found the user who had that weird 49 locale, and then changed it to en, and reran the dead jobs that were throwing the error. The jobs ran without complaint. So this appears to be resolved.
However, the user with the bad locale was not one of the four users getting repeat notifications of posts though he was supposed to get notified about a meeting agenda that didn’t get sent.
I will update my discourse instance again and test everything out again. Cross fingers that getting these tasks to run solves it but I don’t know enough about it to be sure.
ps - for future reference, thanks to @elberet I was able to connect to pg via console: