Hello Daniel,
The exception says that ntdll.dll is asked to execute code from an address from the heap (list) that is not flagged as executable code, using the RtlpTpTimerCallback function of ntdll.dll.
There probably will be an entry in the Windows System logs (Event Log), either in section System or Application.
Maybe its worth checking there for more detailed information, e.g. about the application that called that function in ntdll.dll.
As I am not a developer, I do not know what ntdll.dll is doing in detail, but as far as I found out it is a library from Microsoft that contains NT kernel functionality.
And yes, if the problem only appears if Kontact8 is loaded as a VST plugin, then the issue is pointing to Kontact8.
But my over 20 years as an IT supporter also taught me that, especially in Windows systems, one should never exclude a Windows system issue.
Please find here a guide how to fix ntdll.dll issues.
A damaged system file can be fixed by step 5 and 6.