All right, in case this is useful to anyone else:
@peternlewis had already answered this on a different thread about KM 10.2. The problem is... 1Password! Turning off the "Enable Spotlight and 3rd party app integrations" in the "Advanced" section of the settings solved my problem.
(I should add that in my case, I need to keep that option unchecked in 1P, as it creates problems with KM as soon as I turn it back on).