my cat is very loving but bites

My cat, lady chardonay, is a rescue cat, and has been living with me for 7 years now. She was very bitey when I first got her and wasnt able to touch her at all on a certain spot on her stomach. Since then, she has become one of the most loving cats, always giving cuddles and kisses and always on my lap, but every now and again she randomly bites my arm for no reason at all. I could just be reaching out to picking my drink up from the side and she will bite my arm.

This only happens once or twice a week, but as soon as she bites she will turn away and jump off my lap, but then 5 minutes later come straight back to being the loving cat I adore.

Would love any advice on this because the mind boggles as to why this is happening.

Thanks,

Lizzie B