XenDesktop 1808, since then 2 displays are not working aymore, just one

XenServer 7.1, Windows 10 1703, XenDesktop 1808.2, K1 (I know) GPU drivers on the VDA 369.64, XenServer 367.64
Since the upgrade VDA 7.14 -> 1808.2, the 2 displays attached the Win10 VMs won’t work anymore. Ony one discplay is accessible, although 2 display are shown in the IGEL thin client console, seen inside windows NVDIDA control panel, but not inside a session.The only thing to see is that the task bar is shown/located on both displays, but the 2nd one is not usable.
Graphics profile is set to usage of 2 displays
This setup works sine the beginning (1.5 years).
Is this issue a known one/looking familiar ?
best, Frank

At least you should update to version 4.7 to have at least support for 7.18. There is no support for 1808 at all. See GRID Software for Citrix XenServer Release Notes :: GRID Software Documentation