I believe the "CloudFlare Plus" from Plesk is a specially negotiated deal with CloudFlare which does not include full authoritative DNS only the virtual CName DNS. Disappointing I know.
If I am wrong, I would be glad to hear it! I would much prefer to use CloudFlare DNS.
I suspect this is more...
TITLE:
Broken Netowrk Configuration when Adding IP Address via Plesk on Windows Server 2016
PRODUCT, VERSION, OPERATING SYSTEM, ARCHITECTURE:
Plesk Onyx, Version 17.5.3 Update #4 on Windows Server 2016 (x64)
PROBLEM DESCRIPTION:
Provisioning (Adding) a 2nd IP Address via Plesk Onyx on Windows...