That’s a strange one. I don’t have a RAMPS board so I can’t confirm the code in ramps-updated is working. My memory is a little fuzzy now but looking at the Git history it looks like the ramps-updated branch is just @enducross’s work applied on top of the grbl-Mega-5x repo. I didn’t make any additive changes there – I just used that as a base to then go on to add RAMBo support in the mpcnc-rambo-support branch. Looks like development in grbl-Mega-5x has continued since I pulled in their code so it might be worth looking through their commits since I started my fork and seeing if they’ve made any changes that would have fixed this.
Still, hard for me to imagine what in the code would be causing this on your RAMPS board, but not on the RAMBo boards (which use nearly the same motion control code).