UPD: Fixed it with switching Unicode UTF-8 support off in windows administrative locale settings
Didn’t seem to isolate issue to anything until I started vanilla server, and then got this in the console:
Done (19.249s)! For help, type “help”
08:56:33
Unknown or incomplete command, see below for error
?stop<–[HERE]
Really seems like a bug to me, since it’s not isolated to specific config or plugin or server jar, so I filed a bug report on github: Sleep not working correctly - Minecraft · Issue #997 · CubeCoders/AMP · GitHub