NoScript makes requests to sync-messages.invalid
Using the latest Tor Browser release 9.0.1, my Tor gateway machine's log is full of messages like this:
Nov 19 21:27:11.000 [notice] Have tried resolving or connecting to address 'sync-messages.invalid' at 3 different places. Giving up.
I think this started in 9.0, but I am not sure.
A web search found only that it seems to be an upstream problem in NoScript:
I have not personally verified that NoScript is the culprit. Just reporting what I saw so you can track the issue and make sure to get the patched version from upstream, if/as necessary.