Ok, I think I might have found what the problem was. I was using the Mi WiFi app with a different Mi account than I was using with the Yeelight app. I realized this because the Mi wifi app recognized the bulb as a Xiaomi device and notified me I needed to use the same account to control the bulb (it didn’t recognize the “good” bulb tho). So I did that and now the two bulbs work properly in SmartThings. Very, very strange and obscure solution, but I won’t be complaining anymore lol.
Of course it may have fixed itself since I had to reset the bulb to add it to my other Mi account, but I obviously did try resetting it many times before with no success. Anyways, good talk people of Yeelight :).