Well, this one was sorta answered in the "Mobius" rulings.
From the UDE FAQ:
"[Re:
Stumbling] The effect of "
Stumbling" goes on a chain immediately after a monster is Summoned. As a mandatory Trigger Effect, "
Stumbling" is always on the chain before optional Trigger Effects ("
Mobius the Frost Monarch") or chained Spell & Trap Cards ("
Trap Hole")."
"
Exiled Force" is an ignition effect, not a triggered effect, which means you can choose to use it's effect at any time during a Main Phase, or when you choose to use your Priority to respond to your summon. Now, because "
Stumbling" is a mandatory Triggered effect, it will automatically take up link 1 on the summoning response chain, so the summoning player loses their ability to use Priority for "
Exiled Force"s effect since it's not one of the SEGOC valid Spell Speed 1 effects.
Now, "Mobius" is an optional Trigger effect, so it IS one of the SEGOC valid Spell Speed 1 effects, so it can go on a chain with "
Stumbling".
NOTE: This is how I understand it to be. I could be completely wrong on my above statement! Anybody feel free to smack me down!
So the scenario would be this.
"
Stumbling" is active.
I have 1 monster on the field, and "Mobius" in hand.
You have 3 face-down Spell/Traps, "
Trap Hole" being one of them.
I Tribute Summon "Mobius".
"
Stumbling"s effect becomes step 1.
I choose to use "Mobius" effect, so it becomes step 2.
You choose to respond with "
Trap Hole", so it becomes step 3.
Resolve in reverse order.
"
Trap Hole" destroys "Mobius".
"Mobius" effect will still destroy any remaining cards targeted by it's effect.
"
Stumbling"s effect
Disappears as "Mobius" is no longer on the field to switch to defense position.
Hope this helps!