Why USB CDC fails on open if cache is not enabled?

[AIach.1]

I have created a project with STM32cubeIDE using usb CDC.

If cache is not enabled, accessing via firmware a specific variable located at ox20005604 (for example reading it) once a time, it causes that subsequent open from PC of the serial port returns an error (code 87).

[AIach.1]

Sorry..it is not dued to cache, it depends only on ram allocation

It depends also from boot (sometimes starts working)... i need some more tests

[AIach.1]

I'm using STM32F730V8T6