That's unfortunate. I've seen Another Quality Modpack 2 and 3 rapidly add and remove mods with each update... so it makes sense that other mod packs could be pulling similar plans with their mod selections.
You should back up the mod pack instance before updating, possibly along with the worlds separately backed up. The former action would allow you to restore the original instance if the new version of the modpack is bugged and doesn't work or try to install it in a different manner to see if that fixes it.
Also most mod packs nowadays have a mod that automatically backs up the world. Have you tried checking that?