The error we get looks like

<class 'psycopg.ProgrammingError'>: ERROR: value "20030921115726" is out
of range for type integer select count(*) from _file where
id='20030921115726' 

This happens when I view a message (or an issue containing a message)
with a certain string in it.  I can reliably make the web interface
explode by pasting that string into a new message (which I will attempt
next here)

I think the key detail here is that the message says something like
"I've got the file 20030921115726..." (very long string for the file
name), so I imagine it's got something to do with trying to make a link
to the object 'file2003etc' which doesn't exist.

I tried to reproduce this failure with a postgres backend but can't.

I think this was fixed as part of issue2550549 Postgres error on message
templating

This limits what nodeid's are able to be looked up in the back end.

A similar patch is applied to the backend code for this roundup
instance as well, so I suspect it's fixed here as well.

Closing.