I'm running Debian with Raspberry Pi Desktop (stretch) on my Acer Aspire 5410 laptop.
I have configured the 'Windows' key as a compose key by placing
xmodmap -e "keysym Super_L = Multi_key"
in the ~/.xsessionrc file.
This has been working well for many months.
A few days ago I did some updates (apt-get update, apt-get dist-upgrade), and now following a reboot I have two problems...
(a) The bottom left key with '\' and '|' on it sends '<' and '>' instead. Other keys, including '#~' send the wrong thing too,
(b) The windows key activates menus, rather than functioning as a compose key.
If I use 'Preference>Mouse and Keyboard Settings>Keyboard>Keyboard Layout...', change the model to something else and press 'OK', then change it back and 'OK' again, the '\|' key resumes working properly.
If I then type 'sh .xsessionrc' to reexecute the xmodmap command, the compose key resumes working.
But following a reboot, it's all broken again.
Thanks for any ideas!