assertionerrors from dummy event sending process

[richvdh]

after I lowered the threshold for dummy events (#7413) the logs started filling up with assertionerrors with little clue as to which assertion was failing. I'm fairly sure that wasn't due to my hackery, so this must be an underlying issue. I'd like us to understand the problem here.

[babolivier]

@richvdh Did these errors come with stacktraces? If so, it might be useful to include that here.

[richvdh]

hoping someone else can go and find them ;)

[anoadragon453]

We've decided to close this for now as this is no longer occurring on matrix.org. We can reopen and investigate if it comes back.