alo, not saying this in a "your taking too long" manner. But more or less out of curiosity, what specifically has taken so much extra time within CHP.4 in contrast to the other chapters?
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It's a combination of a few factors. First is that this is a much larger update than 1.4 (the Ch3 map update). 1.4 also included the tabs in the map select menus. This was a feature that took quite a bit of work, but it was the only other major feature in the update. The Ch4 update has 3 features that are as big. It has the animation system (maps can make Susie, Ralsei, and Kris play animations), the save file revamp (it now saves, and displays, more data about your performance) and the Hold Notes revamp (fixing a long-standing inconsistency with hold notes, which was required for the save file revamp). Also while not all maps have full animations, quite a lot do, which means the maps themselves took longer to make. There's also a few other smaller features too, so this is by far the most I've added in an update.
Another factor is that I was kinda burned out after the 1.5 update (the Undertale 10th anniversary map pack), so I did take a break from it. Working on this game on top of covers for my YouTube is a lot of work lol.
The good news is the update is pretty much done now! Just a few small things left to do. I am unfortunately very sick right now so I haven't been able to do much in the last few days, but once I'm better (hopefully soon) it really won't be long!