Generell, wenn ein neuer Kernel mal Probleme macht, kann man einen älteren als Default Boot Option pinnen:
https://pve.proxmox.com/pve-docs/pve-admin-guide.html#sysboot_kernel_pin
Um die aktuellen anzusehen: proxmox-boot-tool kernel list
Wenn die Storages auf den Nodes unterschiedlich sind, musst du das entsprechend markieren auf welchen Nodes diese verfügbar sind. Wenn du ein Storage bearbeitest oben rechts die Nodes auswählen.
Per Default sind alle Storages für alle Nodes...
Set it to warn, then you will see what the ideal would be, without it acting by itself. You should have something in the ballpark of 100PGs/OSD. If you have to few, it can impact performance and also recovery speed/impact in case you lose a node/OSD.
The HW looks good so far.
If I understand it correctly, the PVE hosts connect to the Ceph cluster via 25Gbit/s? While the Ceph nodes themselves use 100Gbit/s?
I would verify that the network performs as expected, as in, do iperf / iperf3 checks...
Some more details would be good to know:
* Disk model of the OSDs
* Network speed for the physical Ceph network(s)
* General specs of the servers, like CPU and RAM
* cat /etc/pve/ceph.conf and cat /etc/network/interfaces please paste the output...