OSI occurs when rented vendors havent yet expired and popped into the house sign giving their owners a certain amount of time to collect the goods and money.
Imagine if you were to play 1m a month to rent a vendor, and then the house owner quit or decided to decay the house by placing another one - that 1m fee is no longer obtainable, all you can do is get the month you paid for by holding up the house decay. Or maybe you regularly log in to make sure you still have time on your vendor, and then find out the contract decayed that day - so you can still get into the sign and get your stuff/money. The delays are annoying and unpredictable to the idoc'r but they're necessary so that vendor renters don't get shafted and get the time they paid for.