I suspect this BZ will be resolved with the fix to https://bugzilla.redhat.com/show_bug.cgi?id=1593663
That BZ relates to validation failures with AMQP credentials that only appears on the 'new' form but not on the 'update' form. It's probably worth re-testing this once that fix is in place.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHSA-2019:0212