unable to package updates for bionic due to missing key

I am aware of the keyserver problems and debated just adding a comment to my open question #670766 also #670706
but this moves from annoying warning to fatal builds.

I can not update my package on bionic. The build dies trying to fetch a non-existent key to verify the diff to the previous release. The only option is to create a new ppa, which works because it doesn't do the diff.
https://launchpadlibrarian.net/378930581/buildlog_ubuntu-bionic-i386.qtpovray_3.80.1~bionic3_BUILDING.txt.gz

Builds for xenial don't suffer this fate.