System.NullReferenceException: Object reference not set to an instance of an object

My colleagues and I are running into what appears to be a .NET error that has been around for some time, but in a new situation.
The software is OpenRoads Designer 2018 Release 3 Update 5.

In certain design files, the error pops up every time we select Corridor Objects > Point Control.
When selecting another point control the error pops up again.
Every time the error pops up, it pops up twice.
I have included a screenshot of the pop-up and the complete text from the error message.

The error is present in all corridors in the file, even a new corridor.
It is possible to create an new point control, but editing an existing one is hard to do and sometimes does not work. Also, when finishing a new point control there are two pop-ups with this error.

The error is limited to only a few files, other files with point controls are working without any problems.
The error is not limited to a certain pc or version of windows, because my colleagues have the same problem with the “infected” files. All files have worked without errors before.
Any ideas to fix this are welcome, because recreating the entire file is not an option.

Thanks, Jan

error pointcontrol.txt