So I saved 30 WE and 100 Loot tickets to farm S4 3-10Hard mode. I have been more than halfway through both WE&Loots to notice I’m not acquiring any Underwild coins for doing this. Pretty sure I should be gaining some.
Just a little note: coins can be received as rewards only for first completion of the stages.
And loot tickets can only be used to replay already completed stages.
You will only get Underworld Coins the first time you complete the stage on normal and on hard.
It should not be mistaken for Atlantis Rises/Valhalla Forever where you can get extra coins by farming.
There may be such event for S4 once all provinces are unlocked.