Thanks for this. After resetting all settings, I realized this is a server-side issue.
I should have mentioned that I sync with open-source, non-iCloud servers that fully support the CalDAV protocol -- one cluster that runs DAViCal 1.1.3.1 and another server running Baikal 2.7. Both these support invitations and replies with Thunderbird's Lightning extension and on Android phones (anecdotally; I have not verified that).
After enabling iCloud calendars and creating a calendar item in iCloud, the invitee list appears for the iCloud item. The Calendar app still crashes when attempting to edit items created on those other systems. After power-cycling the iOS device, editing a calendar item might work once or twice, but it does not show invitees under Edit.