Thanks for the clues. Yes I lost the arrow keys (and other ones) on both the fresh install of 'current' on a new partition and on my older partition. However I had already copied many of the config files in the new partition when I got NOUVEAU running (network parameters, device specific setups, etc). I compile the kernel starting from my day-to-day system .config (after make oldconfig).
I login on a console. I start X11 manually with 'startx'.
Initially, I wished to continue using the NVIDIA driver. It compiled NVIDIA-340.102 against Linux-4.9.44 but the install didn't complete. I tried all the patches people have published on this issue but none worked for me with kernel 4.9.44. So I installed NOUVEAU and I got into the problems I describe in my original post.
I ended up reading a post by a Slackware-14.2 user who installed Linux-4.12 and combined many patches in a single
patch file. That works for me and I am now running the NVIDIA video driver on Linux-4.12.8.
The result is that the arrow keys are back and mplayer no longer freezes when I move or resize a window.
I am left with the message that prints every second on the console (first virtual terminal only).
Changing kernel lead me into another problem though. I lost the the driver of the TBS satellite card (that installed fine on 4.9.44). But that's a different problem.