I have used Paypal and ebay for selling and buying for over 9 years. Paypal is my primary payment receiving option.
Paypal times out on me on a regular basis when I am getting items pulled, boxed up for shipment as it takes too long to get back with the package weight and to print out the shipping label.
So, I would say there is an issue with the website where you are shopping because I am always having to re-sign in due to the very, very short time out that Paypal has preset.
When done with my transactions, I always sign out of Paypal. Have not had one problem in 9 years!
But never, never use debit cards on the internet to pay for anything!