Fence paint with cuprinol

Not sure if this will work, but it is worth a try... Use a solution of caustic soda and water, spray it on and give it a few minutes then pressure wash it off. Use all relevant precautions with the caustic soda, it can be nasty stuff! The previous paint will have made the surface waterproof so the new paint won't adhere to the old. The other alternative would be to paint the fence with a primer first to give the new paint a surface to stick to, or you could sand/wire brush the old fence. Let me know if they work, please.

The old paint seals the fence and waterproofs it, so you could try an primer on top of the old paint first, I would suggest an aluminium primer.

Is the fence dry? Jet washing saturates the wood. It may need to dry. Cuprinol Garden Shades is thin and the lighter colours don't cover fences well. But sounds like its still wet from the jet washing and that's sweating the paint off and causing it to bubble.