Some of the armour has been destroyed but remains equipped on the character model even when I drop it. As in it remains on the character model and I cannot change armour as I get the message "cannot equip while in power armour". Can remove the helmet properly and reequip a different helmet but that's it.

NM saw the solution in the PS4 group. Hold down "E"/use to exit it. So the bug is that you are allowed to equip/unequip/drop it when using it, rather than anything else.