Symptoms
You might receive email notifications containing entries similar to the following.
2. Website "/home/username/public_html" (https://domain.tld): Failed to reset cache for the instance #1
Description
The error message suggests that the cache reset command (wp-toolkit --clear-cache) is failing for some instances. Reviewing the following log file can provide more information. The variable {$date} is the year, month, and day on which the log was generated:
/usr/local/cpanel/3rdparty/wp-toolkit/var/logs/main-{$date}.log
The issue can have many causes, including too low of a memory_limit value.
Workaround
memory_limit value
The memory_limit value for the relevant PHP installations will have to be increased. You can refer to the following article for information on changing the memory_limit value.
How to set or increase PHP INI memory_limit or other values?
Additional Information
The following articles document other possible causes for these errors:
WP Toolkit error "Failed to reset cache for the instance #": PHP Version before 5.6.38
WP Toolkit error "Failed to reset cache for the instance #": Missing site files