Objects on slide not visible

Hi everyone, 

I'm struggling with a specific issue for a while now: sometimes there seems to be a defined area of every slide that is not showing all objects as it should. This area is L-shaped from the lower left to right and right up till down.

On the first slide, the problem is that two rectangles are not shown. These rectangles are possible answers for our users, so in this case they can only choose from 2 of the 4 options. (even more so a problem, sometimes our 'continue' rectangle isn't shown either, which results in the entire course being stuck)

On another slide, an object is only shown partially. You can see that the right side of the dog's head is cut off. This is a bit frightening in a course for children. The advantage is, that this shows perfectly where my 'problem area' starts. The weird thing on this slide, is that both the table and the dog are objects that move in, so I'm unsure why only the dog and not the table is affected. 

This problem also seems browser dependent. I have experienced similar issues in chrome and safari recently and even other browser a little while ago. The problem never occurs while testing in Articulate.

Does anyone have an idea how to fix this (or overcome in the future)?

Thanks in advance!

Best, Niki