HTTP response size mismatch shows in the status column of the Peers tab for a given torrent.
For the torrent in question, Tixati downloaded 154GB of 300GB with speed of 2-5MB/sec before this issue occured.
Other torrents do not have the same issue.
I realize that this most likely makes it an issue with the remote client.

Searching "HTTP response size mismatch" site:tixati.com yields 2 hits regarding language files.

Right-click Connect sometimes works for a piece or two and then back to HTTP response size mismatch.
Right-click Connect sometimes attempts to connect and goes to HTTP response size mismatch.
Sometimes Tixati tries to connect again on its own and sometimes it just sits and does not reconnect.
Most of the time, Tixati is not connected and just waiting.
With 60,000+ pieces remaining, manually connecting is not a viable solution.
Please change the timeout after receiving a "HTTP response size mismatch" message to try and connect again after a second or two delay.

The site and torrent in question are public, so I could email you directly if you wish to test/debug on your own.

Thank you in advance for your support.