Having setup raspberry pi to run as a server, I started noticing that terminating ssh connection will kill the processes I started in it. Some of these were to just serve directory over wifi for easy photo library. This time the difference was that I was tried to kick start server thru my phone (termux) & as soon as I closed the app or moved out of network, server on rpi would die.
In past I just started a tmux session and started server in that. The good thing is that tmux will hang around even if I terminate ssh connection.
Seaching online found that others have run into similar issues. tmux seems to help and there is some good discussion about it here and here. systemd brought this new behavior to all.
But more importantly, tmux works well and here is a very good overview of how unix/linux works with respect to current problem.