I tried to search the internet for anyone else suffering from this same issue, but I found nothing. I run a good handful (30+) of tuning mods, but after uninstalling every mod and testing if the lot would still reset, it did. I tried saving the upgraded design, deleting the bugged lot and putting it back in with all the items that are supposed to be there, but for some bizarre reason the game does not seem to even save my building design completely and would just revert back to the old version.
Anything I had added in build mode remains the same, but all buy mode objects just reset on their own every season. vanish (without being refunded or being placed into my family inventory) and items that existed in the old version but do not exist in the new edition would pop back in. Immediately after this, the entire lot would begin to reset back to its default pre-upgrade self every time the season changes - anything that I had bought on that lot would just. So the basic thing is, I built a custom community lot in my town (Appaloosa Plains) and it worked fine for quite a while, but after some time I decided to upgrade the building to increase its level and the money it'd generate.
I've been dealing with an irritating bug probably related to the Seasons pack in Sims 3.