Hi!
You could also try a reset of your preferences.
Rename the folder prefs in folder 2018 to something like prefs_backup, or to reset everything, the folder 2018 to 2018_backup. Maya creates new folders. Detailed at:
https://knowledge.autodesk.com/support/maya/troubleshooting/caas/sfdcarticles/sfdcarticles/Reset-May...
... i doubt this will change anything, but it's worth to try.
Does it work if you enable it manually in Attribute Editor?
Does it work with a new object in a new scene?
Maybe there is a problem with your keyboard?
