PHP5.6 + PHP7.0 side by side

Hello together,

*tl:dr*
When i execute a PHP7 request over Apache, then the next PHP5.6 request is
blank (without an error log message)

*Long version*
I have two "independent" installation of Apache and PHP on the same
development machine. (both over mod_fcgid)
The only difference is the port :80 for production and :81 for testing

The current one (used for prod): Apache 24-win64-VC11 / PHP
56-win32-VC11-NTS
And the today installed (used for testing): 24-win64-VC14 / PHP
70-win64-VC14-NTS

I had some troubles with opcache on PHP7 so i disabled it for now
-> in PHP5.6 i still have opcache enabled
-> the error msg in PHP7 is:
https://gist.github.com/ThaDafinser/d32c7b84933a2d4eddf1

This strange behaviour is left:
- when i execute http requests for PHP 5.6 everything is fine
- when i execute http request for PHP 7.0 everything is fine
- when i switch from a PHP 7.0 http request back to PHP 5.6 request, the
first request is "blank" and i dont have an error message

My PHP + Apache config used:
https://gist.github.com/ThaDafinser/baa3c2d69898c9d1e31e