I found the reason why it didn't work... :}
One of the reasons was indeed the entry in /etc/udev/rules.d//20-etoken like you explained in your STRETCH.TXT.
But also I had to create the following symbolic link :
ln -sf /usr/local/lib/aksifdh.so.1.3-15.84 /usr/local/lib/aksifdh.so
In my previous (working) installations I never had to do that.
There isn't anything in the logging file where you can see that the etokend service was not working.
The errors for the entries in /etc/udev/rules.d//20-etoken are displayed at startup.
This time I took notes for the future !
Well, the whole experience was very educational , but sometimes frustrating !
I now have a working Eumetcast receiving station running on Devuan ASCII (amd64) ... hopefully for a few years...
And Ernst, thanks again for the help !