Sorry, not ignoring your question, just have no idea. I have looked in every Veg book I have (a fair number) and no one ever mentions 'bitter' potatoes.
Never even heard of potato Tibet.

Sorry should say potato tub, plastic thing. maybe the soil got too dry potatoes are a good size. No idea what variety I just used potatoes that went to seed. My gran used to grow potatoes from peelings they were always ok. I will just put it down to dry soil and hot weather and plant some more. Thanks for looking it up.

Sorry misunderstood. It could well be down to the seed potatoes you used. I would suggest you buy certificated seed potatoes for your next attempt. We have never had much success with growing them in containers, they need far more water than we are prepared to give them to get a decent crop.
A soil based John Innes No 3 compost is recommended for growing them in.

Thank you will take your advice