Tapicall with Octophon Open

We use Tapicall on two workstations with Windows 10 x64 on a Telekom Pctopus Open telephone system with the Alcatel Lucent TAPI driver 6.8.3230.
Tapicall runs smoothly on AP1.
On AP2 Tapicall is constantly unable to connect to Opcopus. Sometimes it helps to uninstall the TAPI driver completely and set it up again, but not always. The computer was reinstalled a few months ago. The problem existed before and still exists after the new installation.

Has anyone had similar experiences and possibly has a workaround?

I still have an assumption: can it be that no 2 devices can communicate with the system via TAPI at the same time?

Many thanks in advance.