The parent zone is not obligated to provide glue records for a delegation if the delegated-to host names is not under the delegated name. Glue records are only needed if a delegation points to something that the delegation would need to be followed for to be useful.
Since you are delegating
gignouser.com to name servers under
eu.clouds.host, that is not the case and glue records are thus not required to be returned by the name servers hosting the delegation to
gignouser.com -- meaning the
com TLD DNS servers.
If you look at the delegation of
clouds.host you will see that the delegation from the
nic.host DNS servers does include glue records.
I do however notice something that may contribute to problems:
You are serving NS RRs with a 0 TTL, for both domains. This can be problematic. If you want to minimize the time that DNS servers cache the delegation data (why you'd want to do that to such an extent I don't know), then serve it with some small but non-zero TTL. I suggest using a minimum of 10 seconds TTL to give resolvers and proxies a chance to do their thing even if they abide by TTLs internally during the recursive resolution process.
I would fix the TTLs first, and see if the problem goes away. It's certainly possible that the report tool you are using is being confused by the zero TTLs.
I also notice that it appears that you are running both name servers on the same subnet -- specifically, on adjacent IP addresses -- which presents a massive single point of failure. If that is the case, strongly consider getting an off-site slave DNS server, especially if you want to serve zone authority data with very short TTLs. While "everything else will be down anyway" is a valid point on the face of it, which error would you rather the users get if your servers are unavailable; "the host name www.gignouser.com was not found" or "the server did not respond"? I would absolutely prefer the latter, even if the end result at that moment is the same in that your web site is unavailable.