If I read it correctly, you were able to sign your modules on F42 again with mokutil, right?
If no, then you may suffer from the same issue I have. Try mokutil --sb-state and see what it says. If it says This system doesn't support Secure Boot., then you won’t be able to sign your kernel modules via mokutil until further notice.
If yes, did upgraded RPMFusion’s repo to 42 too? As far as I know, they have repo’s for each specific version. Maybe this helps.