OK! I HAVE YOUR SOLUTION!
I bought a pair of Birkenstock style clogs when I was in college (becuase I couldn't afford the real Birks LOL

) They did the same exact thing - in the same exact place! WHAT TO DO?
MOLESKIN until you get them broken in!
Use two very small strips (less than 1/2 inch each about two inches long - from the center of the arch to the edge of the shoe with a small space (1/2 inch) between the two pieces of Moleskin to create a 'channel' for the air to escape.
Since mine were clogs - it will work even better for you!
I found that you can barely notice it as you walk - and once the shoes are broken in the slow will become more flexible and allow the air to escape naturally to break the vacuum. BUT - until then - MOLESKIN!
It works!