Heatstroke?

I have a 1999 Volkswagen Passat. It has had some problem starting as in: I turn the key, there is a pause and then it starts. One day it didn’t start at all and I had the battery changed. Same problem. I reset the computers. Same problem. With time, I noticed that it has these problem when it is in the heat (black car parked outside in Florida) and it is fine when parked in the shade, which is not always possible. Any thoughts on what could be causing this?

Thank you!

It cranks but takes longer to catch, or there is a delay when you turn the key and it won’t crank right away?

It cranks, then there is a pause, and it starts.