Wiser and more learned folk will give you a better answer but it will help if you can provide more data by sending the output of the following:
sudo zpool list
NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
alexandria 344G 332G 11.8G - 69% 96% 1.00x ONLINE -
Thanks for the reply. Above line is the most telling data and so I take back what I said before, this is likely the cause given it's your home volume. It's very full!
Your pool is at 96% capacity and 69% fragmented. The 96% is the biggest issue, there is (was?) a rule-of-thumb guid with copy-on-write filesystems, of which ZFS is an example, that you should keep the used capacity below 80%.
> alexandria/home 1.02G 332G 90.4G 242G 0 0
In the pool, your one dataset 'alexandria/home', the snapshots are 90.4G of 332G or 27%, so not the full culprit. The fact the disk is nearly full is.
Possible things to do....
Make a backup first!! or several.
Delete some stuff, clear browser caches, other caches in your user profile.
To clear the fragmentation, copy the data somewhere else, delete it, then copy it back.