Ender 3 x-axis home issue

I've got an Ender 3 that I've had no issues with for months. I've been printing successfully almost daily for some time. Suddenly today after a failed print due to the spool coming off the spool holder (I believe it was printing nothing for a few hours), the homing of the x-axis is not working. The printer is always reading the x position as x=0. Each time I hit "home X" the head moves about 10mm to the right. The display always shows X=0. If I start printing, it will print as expected but with a shift to the right of whatever the starting position is. Any ideas what could have caused this?