Replies to ticket with lengthy history don't send emails

[jlopp]

We recently noticed that the user who created a ticket on 2019-09-25 stopped receiving email replies from us when we responded in Helpy. This ticket has a length history of over 40 replies back and forth.

When I try to submit a reply to the ticket in the browser, nothing appears to happen in the browser, though the console shows a 404 error:

VM450:1 POST https://support.keys.casa/admin/topics/4361-lnd-not-working/posts 404
(anonymous) @ VM450:1
send @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:3
ajax @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:3
ajax @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:12
handleRemote @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:12
(anonymous) @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:12
dispatch @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:2
g.handle @ application-6853e51f7801ffc4ee6c46327bda16c8a8b0b63cf4b84abcf27948589f6a1bad.js:2

I'm attaching the passenger logs as well, which appear to show an error with a user lookup query.
support.keys.casa-1586960584544.log