This may help pinpoint the cause: I did a virgin install of 18.04 on the same machine, and now hplip works, printer is found, printing (and scanning as well) is OK. Therefore the problem must be with the distribution upgrade process.
This may help pinpoint the cause: I did a virgin install of 18.04 on the same machine, and now hplip works, printer is found, printing (and scanning as well) is OK. Therefore the problem must be with the distribution upgrade process.