Not sure what triggered it but all members of my party now "Vulnerable" (double damage) to ALL forms of damage! Luckily during combat the effects are not being applied. I tried many different fixes including console restart, multiple long rests, adding new companions and hirelings (they immediately are infected lol). Respec's either through Wither's or Cheater's scroll have no effect.

Never seen this before. Then again I find there are a lot of strange things happening in Patch 8.

Started a new game which is thus far unaffected.