The computer on the motor - EMM - is not a know-it-all. It only records and memorizes certain items and running history. It is best to be thought of as just another tool for troubleshooting.
Your sudden loss of rpm could be a fuel delivery problem or some type of ignition or timing abnormality and which one has to be determined first to narrow down the malfunction.
Monitoring fuel pressure and using the "flight recorder" feature of the diagnostic software would be the initial troubleshooting step.
It would be best to have a dealer check over your motor for you.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.