Fix is available upstream in Candlepin 0.9.54.14
I've created 2 Orgs, created one manifest for each and uploaded successfully on Satellite 6.3 snap 18. So I am moving this BZ to Verified.
qe_test_coverage PR: https://github.com/SatelliteQE/robottelo/pull/5358
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-2018:0336