Portions of conversations in Gitter are missing in the Matrix room

I recently started a conversion in a room using the gitter.im website. However, when I went to the same room using the Element matrix client, I noticed that there was a line in the conversation that was missing.

Here is a screen shot from gitter.im Screenshot_2021-05-24_at_17.38.02

And here is a screen shot from Element Screenshot_2021-05-24_at_17.37.40

You see that the "Hi... " line is missing in the second.

I have checked this same room using the android Element client, and the same line is missing.

What is strange, is that this room is bridged to a slack room, and the entire conversation was correctly bridged to slack.

Workarounds

When a Gitter user joins a room, we could also join them on the Matrix side instead of waiting for the first message to be sent (as suggested by @piegames). The delay between when they join and send a message is probably great enough to not trigger this issue. But it's still general issue with Synapse which could be triggered at any time-scale given lag and network weirdness.

Related issues:

Edited by Eric Eastwood