Have you recently changed the Keyboard?
No, the keyboard has not been changed. I don't suppose the keyboard could be involved, since the problem only occurs in InDesign.
BTW, just found a simular post, same problem on German version (no solution): What are the shortcut keys Ü and ÿ?
This is what I get:
I found a workaround (actually quite obvious):
Edit > Shortcuts
Create a New set based on Standard, call it something like Standard fixed.
Select Product area > View menu
In the commands list scroll to the faulty shortcuts Grids and guides and replace the wrong shortcuts with the standard shortcut: type in the field New shortcut and click on Assign. On the internet you can find several lists of standard ID shortcuts.
You may delete the faulty shortcut.
You will notice that the correct shortcut is unassigned, which I think proves it is an error in InDesign, perhaps a localization issue?
Hope this will help others.