The fundamental problem with Rodinal is that the pH is critical no matter what you do to mix it or how you mix it.
At the correct pH (which was also rather hard to do back then) there should be a small amount of undissolved PAP remaining in the bottle. If it dissolves, then the solution is too acid and if too much precipitates (more than 1 or 2 crystals) then it is too alkaline.
This will be critical if the concentration is wrong as the pH will then be off as well.
This information in complete form was published elsewhere in another thread with complete instructions.