Hi Thomas, yes that's the link we couldn't post.
I've temporarily decommissioned Server 3 as a test system. It still had an older pre 4.15 kernel installed: 4.10.17-2-pve #1 SMP PVE 4.10.17-20 (Mon, 14 Aug 2017 11:23:37 +0200) x86_64.
Booting with this 4.10 kernel unfortunately produced the...