Hi all, thanks for the follow-up - @IAmGav was helping me in a DM.
Yes, the indexes are an issue - we were unable to restore from a recent backup because of this. We removed duplicate records from a backup (manually) and were able to successfully restore (using the built-in discourse restore cli tool).
The “shared global notifications” are still present - we’re removing the Babble plugin now, will respond when we have more info. The silly thing is we weren’t using the Babble plugin, it was installed but not enabled.
Thanks all for your help!