Did you change your relay list? Likely the new one wasn't available in all relays and if the one relay that had it went down amethyst would only find the past version.
Discussion
Nope, only updated Amethyst, which seems to move the number of relays around. I'm on Tor so unless an old relay now has Tor support, not sure how this happened.
Interesting. Many relays don't work well on Tor. We have plans to do a procedure to resync your events to the newest relays, but it taking a while to finish :(