I ve located the error.
I have imscp php version 5.6.40
i have installed phpswitcher version 5.6.40 and 7.1.xx.
After upgrade to phpswitcher 5.0.3 the software didnt find the phpswitcher version 5.6.40 and this was the error.
Maybe phpswitcher Software have the Problem to differ between identical psw and php versions?
The solution was to set status from all domains which hadnt the Status OK to OK and switch one time the php version which was before set to phpswitcher version 5.6.40 to 7.1 and back to 5.6, and the domain started working.
Now i have no phpswitcher Version 5.6.40, i would need it for the imagick support. But at the moment no problem, because i will switch in a few days to php 7 if i have updated my code.