Though it says it's "on hold", in practice it there seems to have been no further attempts to retest it. reintroduce it or even discuss the problems.
https://community.giffgaff.com/t5/Announcements/PayPal-trial-results-and-next-actions/m-p/22587214 (November 2018) says we will do our best to bring this to life in a way that benefits our members. So, we’re going to continue to work with PayPal on the experience of using PayPal in general
It's weird that giffgaff should have a problem getting payments by paypal when most other sellers manage it all day, every day, without significant problems. So I suspect the problem must be at giffgaff's end, not paypal's.