As telesight said your mount option should look like:
UUID=9e04f12c-4447-4e69-b1a7-48160eecafac /boot ext4 discard,noatime,nodiratime 0 1
So try to replace your defaults,relatime,discard options with what telesight said.
I'm curious as I use SSD's along with UPS for my Proxmox setup, which...