Encypted PM Invalid Topic Key

So I sent an encrypted PM to someone (who had it enabled obviously) and they received it, but they didn’t have encryption on the device they were using enabled so they couldn’t read it obviously. They apparently didn’t even remember setting it up let alone the paper key, so they completely disabled encryption on their current device and then re-set it up. After they did that I then sent them a new encrypted message, but when they open the new one they get a “the message could not be decrypted because your topic key is invalid” red banner, and if they try to reply to it (without reading it) it just pops up the “Sorry error”, error.

I mention the respond error because with the first one (pre-encryption) they could send a response, they just couldn’t see the message now they can’t do that.

Who’s side is the error on? I’m also the admin of the site so I could fix whatever may be broken but I’m not sure where to start…