how to investigate on problem after WP 4.5 upgrade

I have upgraded to WP 4.5. I use the Wp Pro Quiz plugin on my site.
Since the upgrade, I have many display issues with the quiz, such as question numbers and results not properly displayed.
I have deactivated all other plugins but the problem is still there.
It sounds like there is no more support from the plugin author.
I found on the web that there was a Jquery upgrade in WP 4.5, and it was causing troubles to themes and plugins.
WP Pro Quiz uses Ajax, so it may comes from that.
How can I investigate on my own to find out exactly what is wrong?