Calendar shows non-existent task

Calendar 3.04
NextCloud version 22.2.3
Tasks version 0.14.2
lightspeed on shared Linux using php 8.0

A task is shown in the month grid view (square checkbox), when I click on this task, the Tasks app shows with ‘Task not found’.

No obvious diagnostic amongst the hundreds of deprecated messages (!) in the nextcloud.log

How do I go about removing this task from Calendar?