I think the dev said they figured it out, but from what I've seen it seems to be an indexing error when calling a loan variable. If anyone wants to band-aid fix it themselves, go to your "src\core\globals.gd" file and replace this line: (See EDIT for an extra step!)
var newreq = [{type = 'date', operant = 'eq', value = variables.base_loan_dates[i.stage]}, {type = 'hour', operant = 'eq', value = 1}]
with this line:
var newreq = [{type = 'date', operant = 'eq', value = variables.base_loan_dates[i.stage - 1]}, {type = 'hour', operant = 'eq', value = 1}]
I've only tested it with the first loan payment, but the game does the event on Week 3 Day 1 as the custom text in the quest journal says. If this causes problems with the other loan payments (or elsewhere), you can revert the above line back to the original.
EDIT: You also have to edit some code in the "\assets\data\scenedata.gd" file, since the fourth loan seems to check for 86000 Gold and not 30000 Gold. Search for this line:
reqs = [{type = 'has_money', value = 86000}],
and change it to:
reqs = [{type = 'has_money', value = 30000}],
Or you could go for 86k gold and deal with it. I didn't go too deep, so I'll edit this again if this manual band-aid solution has any bugs.