I've noticed that since the jump to 4.1.1, Active Devices on the server dashboard no longer reports anything.
I'm currently running 184.108.40.206 inside a custom FreeNAS jail. I've also tried the current beta in a jail, as well as the 220.127.116.11 FreeNAS plugin. All instances do not show any tiles in the Active Devices area (screenshot attached).
As a test, I installed a server instance in Windows, and it does properly report Active Devices with the current playing file and progress.
As such, I believe this behavior is isolated to FreeBSD/FreeNAS. I should point out that this is FreeNAS, which is FreeBSD 11.2. For all I know, this could be working just fine on 12. I know there are some issues with the older versions of mono and such on FreeNAS.
I've attached a log in which I initiated playing a file, after which no Active Device was shown. To be clear, the Activity section does show stop/start actions, but the tiles that show progress do not appear.