"Lookup CD" button is missing the dropdown that is usually present when more than one CD drive is available.
Temporary workaround: Change the default "CD Lookup" setting; the value does not matter. The dropdown will now show and be populated with available drives. Unfortunately, the issue will again be present after restarting Picard--whichever drive was selected as default on last run will be the only available option, unless the fix is performed again.
I did not have this issue before upgrading from 2.1.*.