Ha.... I made my post without reading page 2, thanks for adding more information.
Just like there are multiple different types of trees and bushes, there are multiple types of tree sap mist. Some Tree Sap mist will liquefy with water and wash off, other types will be just like epoxy paint overspray and be incredibly difficult to remove using clay.
I've come across some pretty tough overspray and when the bond between the overspray and the paint is strong it can be difficult to remove.
You can try plastic razor blades as this would be safer than using steel razor blades and a lot less risky to the paint but these don't always work either.
Chemically removing it is also something you can try. I've actually had good luck using a citrus based product NOT intended for removing overspray but it worked for me.
Stoner XENIT Natural Citrus Mold Cleaner
Even states on the webpage above,
Of course I tested it on the paint first to make sure it caused no harm and if you decide to try this you should test too. I also applied it using a terry cloth wash cloth as the nap of the terry cloth provided gentle scubbing action and do wear gloves should you try this approach.
Also, after you find a way to remove the overspray it's going to be a good idea to re-polish the car just to ensure a clear, smooth surface free from any marring or dulling from the removal process.
Good luck and let us know how it goes...