PDFtron webviewer window content disappears on browser window zoom in and zoom out and never appears again

Question

I am using PDFTron WebViewer version 6.1.0 for a POC. I am facing issue with Webviewer content getting vanished when the browser zoom option is used (ctrl + and ctrl -) in firefox. Once the webviewer content disappears, it will not appear until the page which instantiates the webviewer is fully refreshed. I am getting the below error in console during page zoom.

TypeError: "a.xM is not a function"

Any help you can give would be greatly appreciated.

Thanks,

Syed