Found my issue - had the following in the log:
Feb 26 13:07:12 Mega emhttpd: shcmd (88): /usr/local/sbin/shfs /mnt/user -disks 255 -o default_permissions,allow_other,noatime -o remember=NO |& logger
Feb 26 13:07:12 Mega shfs: fuse: invalid parameter in option `remember=NO'
Feb 26 13:07:12 Mega shfs: fuse_main exit: 3
Looks like I had an invalid config for NFS shares - removed the setting and I'm back to normal.