What could be causing this?

Two different tool paths have different methods. For this one path, the bit spirals down without lifting to the safe Z height after each depth of pass. On another, it raises to safe Z each pass.

What is the “Zig Start Height” under “Add Ramping Moves”? I wonder if that could be the culprit.

Just ramping, doesnt seem to have any effect

From what I can see you 2 different tool paths Profile and a clearance
Profile you have added ramp which will follow a vector
Area clearance you have chosen the offset path and ramping which is fine for both but
you have chosen 2 completely different tool paths
One follows a vector the other does clearance and both react differently