Pulled a fresh rPi3 out of the cupboard and installed JessieLight (2017) on it. Added the file 'ssh' to the root of the sd card to enable the by default disabled ssh; put the SD into the Pi, network cable and power; red LED on, green blinking... rPi3 acquired IP address via DHCP; I can ping it, nmap shows port 22 is open... however, when connecting via laptop on Mint, I get an error: ssh Read from socket failed: Connection reset by peer
If I try to connect from a windows 10 PC I get: Network error; Software caused connection abort
I have no clue what to do next, given this is a new install, on a new Pi, without any other software than the Jessie light image and the file ssh to run a headless pi. I have changed the SD card, wrote image, added ssh file and same result.
There are other rPis (running Jessie 2016) on the network I can connect to w/o problems.
Any help appreciated.
 And no, this is not a duplicate of existing ssh problems on fresh installs.