But then maybe what you mean by luck is that it seems to work for a time, but then stop? If so then that points to script failure - what version of OBSE are you using?
This is what I meant, yes

I am "lucky" in the sense that it won't happen with any specific trigger, and will seemingly stop by itself at times, which can be 5 minutes into a game, or 30 minutes into the game. So I'm obviously "lucky" if I'm trying to play the game and it happens after 30 mins, but "unlucky" if I'm trying to debug it

At the moment I'm using 0019, but I had the same issue with 0018 (In fact, I upgraded to 0019 just to see if it would make a difference). To my inexperienced eyes, it does look like a script failure and somehow that is related to the UL mods.
The thing I'm suspecting is that this issue only crops up when I'm in a UL affected area, which might explain why this failure only happens some times and not always. I am certain I have had this issue crop up within an Oblivion tower however and I don't think there's a UL for that.
The strange part is that of all the hundreds of players using the mod you seem to be the only one that has this particular issue, so there is just no way for me to "fix" what ever your issue is.
I understand. However I did manage to finally replicate the issue in that one save. As soon as you load it with just UOP, CA, UL and MMM, the script will fail in the way I have described. I don't know if you're interested at all in seeing it, but perhaps it can help you figure out why this is happening. If so, let me know and I can upload it for you, and I can even upload the MMM .esm and UL .esp so you can have the exact same environment. No pressure of course, this is just something I hope might help with debugging
if you want to take a look at it. I will continue enjoying your mod regardless