Yup. Ive had a Mk3 regularly crash on me on hot days (30 deg celsius) - my car was dark blue, the trunk got very hot.

The nav would not find the CD, would crash loading the CD, and would really struggle to read it.

Once the car got moving and cooled down, it worked better.

The hotter the nav the harder to read the disc, especially copied discs.

If this is a continuous problem, try adding a cooling fan to reduce the temp around the nav computer.