Multiple vnc/ ftp sessions fail on Rock64

[Maxchess]

I cannot connect by VNC/ FTP from more than one computer on network to my Rock64 but can  do multiple SSH.

Once I have one computer connected by VNC I want to go elsewhere on my network and monitor same session or ftp in.

but once one session is running others are not allowed.

also only allows ftp from computer with other session.

if reboot can connect but loose original session.

how can I allow multiple sessions.