@Scott1568 smart pricing turning on by itself seems to be a new glitch because I've seen another post about it . What you could do is to set min. smart price to your desired price.
Being positive to Covid is one of the extenuating circumstances where guests are eligible for a full refund. Theoretically, they should present some proof but in practice, I don't know if Airbnb requires it . It is certainly easy to falsify one.
You said it is high season so hopefully you will be able to rebook these nights. Good luck