SOLVED:
I had my end stops configured as active-low rather than active high. DOH.
For others following this that may learn from it, here is my incorrect code:
; Endstops
M574 X1 S1 P"xstop" ; configure active-high endstop for low end on X via pin xstop
M574 Y1 S1 P"ystop" ; configure active-high endstop for low end on Y via pin ystop
M574 Z1 S1 P"zstop" ; configure active-high endstop for low end on Z via pin zstop
HERE IS THE CORRECT CODE:
; Endstops
M574 X2 S1 P"xstop" ; configure active-high endstop for low end on X via pin xstop
M574 Y2 S1 P"ystop" ; configure active-high endstop for low end on Y via pin ystop
M574 Z2 S1 P"zstop" ; configure active-high endstop for low end on Z via pin zstop