Sandra, here's a thought....

When i first put on PowerGrip straps, I was so delighted that my feet no longer were able to slip off the front of my pedals when I was careless or when my shoes were wet..... I was so thrilled in fact that I began to ride more aggressively, with my toes pointed down. I revelled in my secure straps, and used to try to mash up hills on my pointed down toes. My newfound "power" went to my head, and I became a "powergrip demon".

This way of pedaling aggressively with toes pointed down naturally pushes your feet forward in your shoes, and pushes your toes against the end of your shoes. This can lead to burning/numbing toes. Not sure if this is what is happening to you, but do try to keep your feet flat while pedaling. Be more aware of when you are pushing your feet against the toe of your shoe. Also, if you are trying to pull up on the straps when you are pulling your pedal stroke up- your feet might not be used to this new thing yet and it may be interfering with your foot circulation. Keep your PG straps a bit loose for a while as you get used to them. There is plenty of time to slowly get used to them and snug them up a bit at a time.
Try to pedal for a while as though you don't have the straps on, without pulling up on the pedals or pointing your toes down....just remember the straps when you are starting and stopping, of course!

In hot weather our feet can swell, especially when we start doing longer and longer rides. Lace your shoes a bit more loosely, or wear a thinner sock.