Turns out that this version had fixed a problem where ZFS ARC cache would only use 50% of RAM on Linux, so now it tries to use as much as possible for cache and release when apps require memory.

Seems like an algorithm decides to use swap for everything else because ARC has higher priority.

Why system has swap in first place? Because by default TrueNAS creates swap of 2GB size on each disk which I left as is long time ago. But this is configurable and should be set to zero.