I'm starting this thread prior to the update today to gather any character issues that affect their performance in PvP and will update based on reports made by others on this forum. I'm sticking to just bugs, not weaknesses.
1. If you use 2 of the same character, the damage is reduced by almost half. This happens only when they both have the same star value and level. In addition, you'll gain XP for a character not taken into battle if you have 2 of the same character with same star value but different level.
2. The Sentinel Golden Son skill "Dancing Sun" provides the heal shield visual effects, but it doesn't actually reduce damage nor heal.
3. Stone Talismans do not increase your Def stat when complete a set.
4. If you play other games on your mobile device, (F'n) Visions Eddie will appear in your other game at random times and kill everybody.
I will add more issues when people report them (especially post update).