My experience with modding so far is that the key to keeping the bugs in check is to playtest frequently after adding only a small number of new events. That way you haven't added enough code to really fuck things up, you'll have a small number of bugs that will be pretty easy to fix, then you move on to the next set of events. So you don't code the entire release and then do the bug fixing at the end. You do both at the same time. It's MUCH faster that way. Usually a few broken links or whatever will still slip through the cracks, especially on paths that you don't personally like as well and for that it really helps to let your fans know that you will actually respond to those bug reports.
The problem in this case is the game not being a VN, but sandbox, where the order in which events are played, is not given.
The event to get rid of Eric had some unforseen consequences, his face would appear on schedule in certain rooms, even if he had already been kicked out.
You can say about Aleksey what you want, but he is not great when it comes to planing ahead. That Eric would be gone at some point was always known, so these scheduled events should have included a check from the beginning. But as it is, it had to be added later, which causes more work and more potential errors. Usually a dummy check is used that always returns true if it's not yet known what the check will depend on. So once it's known, only this check has to be altered. But if it's not in the code from the beginning, it can be a pain to find all the places where it should be.
Such mistaktes are one of the reasons there were so many bugfixes.
Some others were related to translations, those don't count.
