Updates to the plugin never get released without testing. But unfortunately we are not able to test every possible scenario.
Version 5.6.0, released a week ago today, added the Convert ICS Calendar Blocks utility, to handle the deprecation of the ICS Calendar Block. To make sure admins were aware of the issue, that version also added a check that scans site content for the presence of the ICS Calendar Block, and displays a notice in the admin area.
That check was coded to only run at most once a week, and in testing it was effective. However we’ve learned that there are some situations where the transient for tracking when the check has been run wasn’t always reliable, and the check might, as a result, run on every page load.
Since the check requires a database query, this could quickly have a major impact on performance. While we don’t yet have a new means of running the check, the top priority was to resolve this potential performance issue. Version 5.6.1.1 removes the check entirely (except during the initial activation of the plugin after the update).
If you are running 5.6.0 or later, please update to 5.6.1.1 ASAP to resolve this issue.
—Scott