Another issue with OA.. Charmed by the Harpies on the beach, and made party members that were in melee with other Harpies move away from their targets to go to the one charming them. This triggered OA each time. 5E rules would not grant OA when the subject is moving out of their control, such as a Push/Shove or being Charmed.
Additionally, Charming a target should not trigger attacks since the target is now Friendly toward your allies, unless you charmed them explicitly to gain advantage (which is valid) on them or with the intent to cause OA's or other type events, (with is not valid)
This makes me agree with the previous poster, that OA has been setup slanted poorly against the player. And this encounter shows that both OA and Charm need work, as the AI is using both in a way that plays one off anther against 5E rules.
