Eperiencing fluctuations while opening an app

Hi there,
I am using an android phone. I have registered for a free trial of the checkmate app. It was working fine but now my mobile has started experiencing some fluctuation while opening the app. This error not only occurs with this app but other apps too. What could be the reasons for this sort of fluctuation? I have read that it might occur because of the updated OS not being able to decide between the updated CPU and the GPU. But I haven’t updated my OS so far. Could it be any virus or malware? What should I do to avoid these fluctuations?