Same firmware version as me, but I’m not using the zen kernel. May I ask if you are using luks?
As an update: I found multiple forums (Including one from frame.work) having the same issue, with many giving advice to run fstrim. I thought I had trim working, but it turns out LUKS does not allow trim unless you pass a kernel parameter to explicitly allow it (I guess for some privacy reason). I have since fixed this, but only 35GB was trimmed, so not sure if this was the issue. I’ll report back if it happens again and I’ll run dmesg.
edit: Turns out it actually trimmed around 1.5 TB.
Thank you everyone for your comments!