Website Bug Fixes and mobile speed improvements

I have experienced major issues with my site www.wefindcarsforyou.co.uk after recent plugin updates. I wasn't sure which plugins caused the issues, so I deactivated/re-activated them individually to try and ascertain which was the culprit. This however only worsened the issues. The mobile site (most important) is not working properly at all.

Issues I noticed after the initial plugins update, but before I deactivated/re-activated all the plugins:
The testimonial section of the website stopped working, it would not load. See attached screenshot (I have currently disabled this section)
There was a logo in my contact us section above "All Rights Reserved" This has disappeared.

Issues after I deactivated/activated the plugins:
Testimonials still not working. Desktop site seems fine other than this and the missing logo above the "All Rights Reserved."
Mobile site taking extremely long to load.
Slider Revolution slider not loading/displaying on mobile.
The mobile menu burger does not do anything.
The call to action buttons, "Lets Get Started" and "Find My Car" are not showing on the mobile.

I have also just discovered that if you press the submit button for the enquiry section towards the bottom of the page on the mobile, it loads the site quickly and predominantly displays it how it should be or how it was loading previously!?

I am looking for someone with a good amount of experience to help me with this issue.

Many thanks

Matt