Null variables

In my title, I have a number of variables for the score, the date, the title name etc. I used the same framework already for various titles.When I preview the course I am working on with a publish to HTML, the variables are sometimes displayed, other times "~~~null~~~" is displayed.Initially, I was thinking I messed up my framework, but it even appeared to be with courses I did not modify and courses I even did not create myself, such as Benjamin Pitman's Tool Kit. Next, I did a test on a colleague's pc and there it did work. Does anyone has any idea what is wrong on my pc? I suppose it is a pc-specific issue. I already deleted my temporary internet files, but that did not resolve the issue.