P0446 code and then warning lights and red triangle

Hi all- hoping to find others who have experienced this issue, or have knowledge to share either way. Have been having an issue with my 2005 Prius (146k miles) throwing the P0446 error code (Evap Emission Control System Vent Control Malfunction). Happens primarily when the gas tank hits just below half. Opening the gas cap and reclosing it tighter works, then clearing the light, until the next time the tank hits just below half when the light comes back on. Assume a seal needs to be replaced, but I'm procrastinating b/c I just sunk a lot of cash into two new ball joints.

Last week the light came on and I just left it, meaning to run the code and then clear it. I did open/close the gas cap more tightly, just didn't run the scan or clear the light. Today I got gas, about 1/2 tank to fill it, and then closed the cap tightly, check engine light was still on and I made a mental note to clear it when I got home. After 30 seconds of driving, multiple lights popped on including the red triangle. Car was running fine, so I continued driving the 10 minutes to home. When I arrived home I connected the scanner, cleared all the lights, everything went away. Powered on and off several times, still clear. Drove around for 12-15 minutes, still clear.

Seems to much of a coicidence with the timing of getting gas to have this not be related to the gas or gas cap, but would that cause the triangle?

 

I doubt the scan tool I'm using shows hybrid system codes- so I cannot say. The P0446 is what has been causing the check engine light to pop on every month or so for about 6 months now, and thats also what came up today. When I cleared that code, it cleared the check engine light as well as the red triangle, neither have come back on.

 

Turns out a family member did have an OBD bluetooth plug in scanner- it did not find any codes, likely because I cleared them when I arrived home earlier. I plan to drive it locally through the neighborhood tomorrow, but not sure what other than the code related to the fuel could have triggered the red triangle. gas mileage still at 56mpg, 7 out of 8 bars on the battery consistantly, no performance issues.