That is helpful Raksj04, thank you.
A strange thing happened when this EVAP issue became a real problem. After refueling I was having a difficult time restarting the car. Also the engine idle would drop at stop signs, and stall out (those are very common symptoms.) What's strange is that after I changed to non-ethanol gas, those problems were greatly reduced.
The idle will occasionally stutter at stop signs, but it's nothing like it used to be. Who knows,,,but changing to non-ethanol gas seems to improve drive-ability during this particular EVAP problem.
If I understand the system correctly a stuck open purge solenoid could cause a vacuum leak. Here is a link for the TSB that covers the P0455 code. https://www.miata.net/garage/tsb/01-023-10.pdf
Having a troubleshooting guide, makes fixing stuff like this way easier. lol