Well yes certificates are not responsive . They are based on strict and width and height .
In mobile they cannot be opened for the first time only .
The problem is actually we are using a script that takes screenshot of the certificate html that is generated .
As certificate is based on fixed width and height in mobile it always left short of width , script runs and takes screenshot of this certificate without knowing that it is being cut off from screen .
What we can do is prevent user to open certificate in mobile and ask them to view it on desktop for the first time only .for this you can use this tip :
https://wplms.io/support/knowledge-base/add-notice-to-view-the-certificate-on-desktop/
Once the image is viewed on desktop , we save this image in media library , then user can open it on mobile .