Quoted from gweempose:
This is a design flaw which is not limited to the pro. I've seen this happen on the premium/LE as well. When I do the combo, the ball will sometimes do exactly what you are describing, where it jumps off the Arena ramp and comes back to the right flipper via the BG return ramp. Other times, it will travel behind the playfield and then jump off the ramp as it re-enters the playfield. When this happens, the ball can get stuck behind the flasher dome near the diverter magnet.
That's kinda depressing to hear; the two TWDs I played (prem and a pro) didn't seem to have this issue. Has there been any kind of tweaks to fix this? I imagine softer coil power will help and/or different type of rubber. Different color or super band?