WPMU Error on several sites

I am getting the following error in several sites debug.logs

[21-Feb-2017 11:51:21 UTC] [WPMUDEV API Error] 4.3 | Error unserializing remote response. ((unknown URL) [500])
[21-Feb-2017 16:59:31 UTC] [WPMUDEV API Error] 4.3 | Error unserializing remote response. ((unknown URL) [500])
[13-Mar-2017 23:41:53 UTC] [WPMUDEV API Error] 4.3 | cURL error 6: Couldn't resolve host 'premium.wpmudev.org' ((unknown URL) [500])
[14-Mar-2017 12:12:49 UTC] [WPMUDEV API Error] 4.3 | cURL error 6: Couldn't resolve host 'premium.wpmudev.org' ((unknown URL) [500])
[24-Mar-2017 11:56:25 UTC] [WPMUDEV API Error] 4.3 | cURL error 6: Couldn't resolve host 'premium.wpmudev.org' ((unknown URL) [500])
[24-Mar-2017 23:42:40 UTC] [WPMUDEV API Error] 4.3 | cURL error 6: Couldn't resolve host 'premium.wpmudev.org' ((unknown URL) [500])
[02-Apr-2017 12:07:04 UTC] [WPMUDEV API Error] 4.3 | cURL error 6: Couldn't resolve host 'premium.wpmudev.org' ((unknown URL) [500])

Please note that it is over several different days. How do I resolve it please.