The triggers_to_buttons is no longer applied automatically to the xpad driver , since it breaks the Xbox controllers mappings in SDL and subsequently any applications that use the SDL's GameController subsystem. Existing installs are not affected, but new installations will not get this configuration automatically, though you can manually add it and will stay configured.

EDIT: how did you try to map the Z/C buttons - to which gamepad inputs ?

So, if anyone cares... Went back to an old image, upgraded everything and went from there. Seems to all be working. I don't know what got out of sorts.

I'm glad I figured out that the latest version of Retroarch saves controller configurations as overrides. That took a minute, but now trackball and spinner can both work as appropriate.