I've had an issue with Granthes' OMSP and other OMSPs using the script class (tipsy & resizers) becoming visible every few days, on every single lot in the world. Currently the only way to trigger invisibility again is to enter build/buy, but that is very tedious with the amount of lots and frequency in which it happens.
It also happens with objects that I've added Buzzler's VanishingObject Script to, but re-triggering invisibility for these objects universally can be done in a few clicks to a single object, so it's not too big a problem.

I've requested that Buzzler add the OMSP class to the VanishingScript supported class list, but he hasn't been active in a while and I'm not sure he'll get around to it.
So, is there a way anyone can think of to stop the OMSPs from becoming visible constantly?

I don't know. maybe a mod conflict? do you have any nraas mods?

Yeah I do, almost all of them. I checked my folders with Dashboard though and it doesn't show any conflicts.
It happens after lots get reset. If I click NRaas>Master Controller>Rest Lot, everything refreshes but the invisible objects stay visible afterwards. I figure Overwatch is, for whatever reason, resetting lots every few sim days.

This is an excerpt from Buzzler's Vanishing Script update notes: "2011-06-30 - Added classes. Added nightly alarm to recover the visibility state if it was lost for some reason. Added coding so objects should stay invisible on reset, or at least become invisible again immediately."
Didn't seem to fix the problem though. I should note I've got the latest versions of the mods and I've also done some testing but was unable to replicate the problem in an empty world on and an empty lot. It only happens in a full world on a furnished lot.

It doesn't happen to other invisible objects like the EA Buydebug lights though, so I wonder if it's possible to take whatever coding they use for the invisible function and implement it in the others?

Ask the guys from nraas about the issue

Good idea, I'll do that