I believe I have found a cause for the error that happens when a Monopoly game is blocked.
Last night, I played a game resulting in me having negative $2038 on the super board and a few monopolies.
Every property I own has structures built except one property in each group has a hotel while the others have houses.
I attempted to mortgage my utilities as well as railroads in hopes of breaching the zero mark so I could roll the dice, continuing my turn but that hasn't been successful.
Since the house stock is exhausted, I can't sell a hotel and neither can I build a hotel to increase the house stock because of my negative balance.
Not even mortgaging is possible as the game doesn't allow players to sell built-on properties back to the bank let alone complete monopolies and trading most likely won't work if the game disallows this particular type of transaction.
I just want to put this message out there in hopes of letting players know that situations like this are indeed possible to attain.

I said that in my last post, that game is pretty much screwed. From what I know, you’re going to have to sell one house at a time. For example, on the three properties that you would need to sell houses for, you would half to start selling one house on each property one by one and refreshing to sell houses dialogue. That’s all I know for now.

Hi, this is not a bug here, it has been discussed before, if you are playing in the real life you would be stuck too, as there won't be houses to cover your removed hotels.
When you remove a hotel, you have to replace it with 4 houses which was not available, so in this case you had to sell all the houses first or at least 4 of them so you can remove a hotel.

Was it also impossible to sell houses on properties where you didn't have a hotel?

It was indeed impossible to sell houses on properties if you had a monopoly where one property had a hotel.
The game forces you to either build or sell buildings on properties equally.

I have not had this issue for ages but if my memory is right then there is a strange solution where you have to sell houses from other properties you have before you can knock down the hotel you intended to knock down in the first place.