Looking closely at the Aptclonesystemstate file we can see that the installed version of libavfilter6 was actually the bionic version installed on artful.
686 libavcodec57 7:3.3.4-2 1 687 libavfilter6 7:3.3.4-2 1 688 libavformat57 7:3.3.4-2 1 689 libavresample3 7:3.3.4-2 1 690 libavutil55 7:3.3.4-2 1
This certainly caused the failure to calculate the upgrade and is not something we can fix.
Looking closely at the Aptclonesystemstate file we can see that the installed version of libavfilter6 was actually the bionic version installed on artful.
686 libavcodec57 7:3.3.4-2 1
687 libavfilter6 7:3.3.4-2 1
688 libavformat57 7:3.3.4-2 1
689 libavresample3 7:3.3.4-2 1
690 libavutil55 7:3.3.4-2 1
This certainly caused the failure to calculate the upgrade and is not something we can fix.