Any news on this?
As I am having the same problem on several Proxmox installs with ZFS (2node Clusters, v4.latest, AND even with new v5.0!).
Servers are DELL (different Modells, R815, R630, R410, .. ) with different HBAs, Disk-Drives/-Brands and even CPU-Architecture (AMD, Intel).
Symptom(s)...