iOS Mail Turns off SMTP Server if two or more are listed iPad iOS version 11.2 (latest update).
Two different email accounts on this device.  We use third party SMTP providers (mailgun/sendgrid) for email deliverability/trackability stats.  Each address should have its own SMTP credentials.  Am able to successfully set up SMTP for each address.

However, here's the problem:  Set up the first address SMTP, set to primary server (on).  Then, go to second email address SMTP, set up, when this is set to primary for that address, the first email SMTP is turned off.  Reversing the process produces the same result.

Even if no primary is designated for each of the addresses, and setting a alternative STMP ON to a corresponding email, the behavior still occurs.  

SMTP accounts with identical credentials have been tested and working on Linux, Windows Outlook and Android with no problems.

Any workaround for this?  SMTP manager app?  Other ideas?
Rebooting the iPad mysteriously solved the problem.