Actually the chat archive is still there, at least to me if I goto "chat archive' link on the campaign.
Dont think its cached on my side, as I just tried in firefox and never logged into roll20 with it, and can see it.
Its not a big deal as far as urgent, just not sure why it wont clear.
Actually noticed this, is the the one line I get in debug log after it fails for me:
Failed to load resource: the server responded with a status of 502 (Bad Gateway)