Based on this thread it's the deduplication that requires a lot of RAM.
See also: https://wiki.freebsd.org/ZFSTuningGuide
Edit: from my understand the pool shouldn't become inaccessible tho and only get slow. So there might be another issue.
Edit2: here's a guide to check whether your system is limited by zfs' memory consumption: https://github.com/openzfs/zfs/issues/10251
I'm in the same boat, but didn't jump so yet. I've been following paperless for a while now but every time I look at scanners I'm blown away by their prices...