You may see an error like this from time to time:
[:error] [pid 13411] [client 220.127.116.11] ModSecurity: collections_remove_stale: Failed deleting collection (name "ip", key "18.104.22.168"): Internal error (specific information not available) [hostname "www.someurl.com"] [uri "/wp-content/themes/businesspro4/cyberchimps/lib/js/jquery.slimbox.min.js"] [unique_id "WnwuNNIzDK0AADRjrMoAAAAE"]
This is a benign error message, and it can and should be ignored.
Modsecurity has a system called collections. It basically allows you to create arrays, and store,information. For,example,you can count the number of times something occurs over a lond period of time, say you wanted to count the number of times a page is accessed over a week. These arrays can also be time based, for example an entry might expire after so many seconds or days. So it stores this in collection files, really lite databases basically. It also has the ability to remove things from those arrays. This only occurs when a request occurs, because modsecurity has no execution logic like a normal program might, it’s trigger based. Sometimes when a trigger occurs are it wants to remove an entry from the database it might already have been removed by another thread. They are harmless.
The message used in the example above means that thread tried to remove that entry from a collection storing up addresses, and that IP address has alaready been removed by another thread.