4 blinks is a focus error. It seems to focus ok for reading, and the self test passed, which involves focusing for writing, so it could be media. You said it does not happen every time. I'd try a TY or Verbatim disc to see if it works on "recommended" media.
Plextor recommends against lens cleaning discs, says air flow should be enough to keep it clean. If you use an abrasive or contact cleaner, it can scratch the lens. If you use a disc with a brush it can knock the lens out of alignment.