We installed salt-treated wooden railing at the entrance to our our home, several years ago, and it was primed within one year, but never painted. Then two years ago, the railing was finally painted, but the paint started popping and splitting all over the place. Last spring, we added more detail to the wooden railing again, and we painted again. The new paint on the new wood is holding up just fine, but the paint has again popped and peeled so badly on the older parts that there are horizontals that no longer even have paint! What can I do to fix this so that it will last for longer than one year?
I am concerned you have several issues. I have not had any experience with "salt-treated" wood but it sounds as though that by itself could cause many of your issues.
Additionally, the primer should not have been left un-coated for longer than 3 weeks.
Hopefully after this time, if you will re-prime the bare wood, then apply 2 coats of good quality finish you will find all is better.