I don’t think it’s the overshield breaking , I think it’s the 75% threshold at play just looking at grinder not lua.
The overshield can break but your max threshold from the shout is still increased and it can be refilled, so it changes the thresholds if a shout buff is active irrespective of having yellow bar. I think there may be bugs some math bugs in there or what it considers missing and I haven’t looked deeper yet.
If you have a poxwalker nearby you can kill it and increase your tuf past threshold and watch it change.
See the TDrX top left at 1.00? I still have overshield.
Soon as I gain tuf the threshold for Iron Will is valid again and TDrX drops to 0.50 as expected.
If you use the default Creature Spawner mod and give yourself multiple shouts w/ ult reset hotkeys you should be able to see it by taking dmg.
And when 1 shout expires, the new max will take effect, threshold will change and TDRX will adjust accordingly.
Could be I’m wrong somewhere or misunderstanding and there may be more weirdness, I shoulda been asleep hours ago…