Error in reverse signature: Failed to verify/extract sig: Message wasn't signed

#6512, #4754 seem like they might be related. I updated the expiration dates of my keys earlier this year, but the failures started just a couple days ago. Not sure what the appropriate steps are to track down the precise cause of the failure; It sounds like it could be either a Go wrinkle or something about my keys?

Start by comparing this report with related issues #6512 and #4754, then reproduce the reverse-signature failure using keys whose expiration dates were recently updated. Done means isolating whether the failure comes from Go behavior or the key material and documenting the precise cause and next steps.

Written by the indexing model from the issue text.