High Availability with local ZFS storage

[esi_y]

When I reboot a host, a FRESH replication occurs instead of making a delta and it takes forever.

It's weird, but I have seen this issue on the forum several times in the past, e.g.:

https://lists.proxmox.com/pipermail/pve-devel/2021-November/051094.html

I would suggest to file Bugzilla report on your case with details, there might me more bugs like that around still.

https://bugzilla.proxmox.com/