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Hi @onhate and thanks for your contribution!

I was pretty puzzled by this bug, because as we can see in the logs of the bug report, it should not actually send work to the worker thread doing the publishing to SQS:
No messages match filter policy, not publishing batch from topic 'arn:aws:sns:us-east-1:000000000000:<redacted>-events.fifo' to subscription 'arn:aws:sns:us-east-1:000000000000:<redacted>-events.fifo:71de2566-97e6-48b8-a222-54c9adadcf96'

However, after looking, it seems we have a deeper bug in there: while filtering the messages for the subscriptions, we modify the context we send to the workers while it is being processed, which leads to the issue. This PR would fix the error messages but still subscribers would not get the messages because it would be filtered when it should not, so we need to fix the underlying bug first, and then no worker would receive an empty message entries anymore.
I also wonder about the fact you had to restart LocalStack as well, as it seems the exception was handled and logged, so maybe something else is amiss here.

Would you mind if I open this bugfix PR pretty quickly, as it's quite a serious bug?

thanks for the quick response @bentsku
I would love to see a fix to this and learn more about how it works :)

Hey @onhate !
I've opened #7674 now and I tried to explain in detail what lead to your issue. I'm really grateful for your report!
For how we structured the publishing code for SNS, here's the PR refactoring it to the current implementation: #7267 (and here's the S3 Notification PR mentioned #6903, introducing this pattern across our codebase).
If you have any question about something in particular, do not hesitate to ask!

Thank you very much @bentsku for the quick actions, I went through the code changes and I am glad I could understand it all :D