Vertical slider in column H5P - iFrame - Resize

Hi all, 

For our client we have made a course in H5P and embeded the code into a HTML page so that we could add buttons etc. 

All of our developpers on different machines and different browsers experience diffents issues. At mine, it's almost all the time correct. No slider, just everything on screen. But my colleagues and my client experience, out of the blue, something different. They get a slider, vertically. Mostly in the column of H5P. We have an interactive video and below an accordion. Sometimes the video isn't fully on screen, on some there appears a vertically scroll bar which doens't make it any easier for the students. 

We have tried a lot of options. From changing the iFrame, to the width and height in the embeded code, but nothing seems to work for every device. 

Does somebody please have a solution on how to make this work properly on every device and browser? 

Hope you can help. 

Thanks in advance.