vs2017 native code debugging exception calling unmanaged code

I'm calling a properly declared unmanaged C++ DLL from VB.NET as so:

input = 1 ' line 1
ret = myclass.ouch(input) ' line 2
ret = ret + 1 ' line 3

This works without a problem and the output is as expected. I then wanted to debug my code. I set a BP at line 1 and step over (F10) to line 3. This again worked without a problem. I then enabled "native code debugging" and did the same thing again. However this doesn't work anymore. As soon as I hit F10 (step over) on line 2, an exception is thrown in ntdll.dll (access violation writing location 0x).

Eventually I was hoping to be able to single step into the unmanaged function using F11 (step into), that also doesn't work with the same exception. However I'm very confused as why step over doesn't work either.

Also I was trying to set a BP inside the DLL code, however I can't do that because apparently "no symbols have been loaded for this document". That is another thing I don't understand, as the DLL is compiled with full debug on and it's properly included as a project in the solution.

Is there anybody who has an idea what the problem could be? Keep in mind, executing the code normal, without debug stepping over, works fine.