[youbetcha]

It's possible that out-of-town station #1 filled your tank more than normal, so your gauge to stayed at "F" longer than you were used to (mine stays all the way to the right on "F" for 3-4 gallons). Then maybe out-of-town station #2 was too sensitive, and stopped filling way too soon, and put 10 gallons in even though 12 - 14 would have replaced what station #1 had put in there.

Plus, you could have been fooled a bit because you were driving somewhere new, the first time where you say you used "1/2 tank" based on "miles," you could have been pretty far off.

I would fill it up at your usual station next time, you've probably only gotten 9 miles to the gallon since visiting out-of-town station #2.

Also, my '07 Pilot has no metal flap with a spring.

 

[youbetcha]

As for the metal flap that was just a guess as to what could have been causing the problem since it vanished about the same time the problem started. It's possible it's not related at all and is sitting in the bottom of the gas tank not causing any problems.

I don't think there ever was a metal flap. There's a fuel cap (and the exterior door on the body) but that is it. Is anybody else's different?

Looks like that is it on the owner's site diagram, but it's not the best image.