I had the same problem with mine and two body shops have repainted it in the past but couldn’t stop the paint lifting after a few weeks. I removed all the paint right back to bare metal, the top surface is aluminium and the frame underneath is steel which causes a reaction. The bubbles on my spoiler were caused by tiny holes in the aluminium caused by this reaction, I had the same problem with the doors of a Range Rover for the same reason. I don’t know what the solution is but I’m considering wrapping it, I’d be grateful if anyone could suggest a permanent solution. Thanks