Either you're filling the entire drive, or it's dying.
https://doc.pfsense.org/index.php/Filesystem_Full_/_Out_of_Inode_Errors
Having multiple sites seeing the same thing, and seeing the same thing after putting in a diff SSD, doesn't necessary narrow it down. It's rare, but we have seen instances of people buying SSDs in bulk where the entire lot of 50-100 were bad and would fail along those lines after running for a handful of days. A power cycle would make it last a few more days. Eventually those were confirmed with the manufacturer to be a defective lot.