Discussed with David on IRC, he has another problem which isn't related to what is reported in this bug.
This bug was fixed in OSP10 but I confirm it's not in OSP8 or 9. We close it now.
I'm closing this BZ as I found out what was the issue on my side. My hypervisor host (which runs undercloud/overcloud) had an offset clock and when booting the overcloud nodes on the first time, ntpd would sync back the clocks of the overcloud to +2 minutes or something close to that with the default ntpd configuration. Maybe ntpd shouldn't be enabled by default in the overcloud images and should be instead configured by puppet/ansible later on but that'd be another case.