pkg: cached package *:size mismatch, cannot continue

[unicorn]

when I run pkg upgrade,I get an error:
pkg: cached package os-generic-userland-devtools-20.06.01: size mismatch, cannot continue.
so I run pkg update -f,and then pkg upgrade,failed again.
I unselect os-generic-userland-devtools-20.06.01 in update-manager,but upgrade still failed.What's going on?

[ericbsd]

this was probably when the server was in syncing.