Traditional Webvpn rewrites the page and sends it back to the user. So if there are custom scripts etc running on the page, it may not always work as expected. One thing you can try is go to the latest ASA release to see if this fixed. Another option for situations like this is Smart tunnels. Smart tunnels still send traffic through the VPN tunnel but they are proxied rather than re-written. So the page content should be pretty much similar to original one.
We are running the latest IOS for the 5525X, so we cant upgrade from what i can see. I had tried the smart tunnels but it doesnt seem to work either. The page loads but i just cant click on any email. Google drive also just hangs on login. It can get the the page just wont display
Is there anything else you could recommend? I am looking at having to use basic HMTL?