Sorry for the late reply,
yes uefi+secure boot.
I Installed the Server on 10.Okt.2023 at 16:09:27, with Kernel 6.2.16-3, Debian 12.2.0-14 (Thats info from the oldest boot log)
So it was the Proxmox 8.0 ISO.
there is maybe broken text in the...
Do you remember when the breaking systems were initially setup? - there were changes to how booting is handled for btrfs installs during PVE 8.0 - so it would help to know which ones make problems for you.
* Are those UEFI or legacy BIOS setups...