Errors that are showing up in the error log

I am not sure what is initiating or causing the errors, but I am seeing the following:

[01-Nov-2017 03:34:21 UTC] [WPMUDEV API Error] 4.4 | cURL error 28: Operation timed out after 15001 milliseconds with 0 bytes received ((unknown URL) [500])
[02-Nov-2017 15:30:53 UTC] [WPMUDEV API Error] 4.4 | cURL error 28: Operation timed out after 15000 milliseconds with 0 bytes received ((unknown URL) [500])
[06-Nov-2017 17:05:16 UTC] [WPMUDEV API Error] 4.4 | cURL error 28: Operation timed out after 15000 milliseconds with 40713 bytes received ((unknown URL) [500])
[06-Nov-2017 20:59:24 UTC] [WPMUDEV API Error] 4.4 | cURL error 28: Operation timed out after 15000 milliseconds with 25763 bytes received ((unknown URL) [500])
[07-Nov-2017 10:46:54 UTC] [WPMUDEV API Error] 4.4 | cURL error 28: Operation timed out after 15000 milliseconds with 29154 bytes received ((unknown URL) [500])
[07-Nov-2017 15:30:52 UTC] [WPMUDEV API Error] 4.4 | cURL error 28: Operation timed out after 15000 milliseconds with 37939 bytes received ((unknown URL) [500])

Please advise what needs to be done.

Thanks!
Paul.