White rectangles when using drop downs

I'm having trouble with my drop down activities. When I click the drop down to select an answer, randomly a white rectangle appears and covers the text. It looks like a bug but I'm wondering if there is at least a temporary solution to it.

Using Storyline 2 developing custom assessment but using the generic drop down activity. I'm not sure I can attach the link to test it because of client confidentiality - but maybe have a look at the image if anyone has had similar problems?

I have submitted a support ticket to try and resolve this also.

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