Hi, I Want to Ask about my website that use DNN version 7.0.5

I currently experiencing session swapping in our website. that sometimes when some user login, they get other user session. And this case is happened intermittent. We cannot seem to find the root cause of this problem.

our website is located on Intranet and the user is connected to a Proxy Server before connecting to our Website Server.

is there anything that need to be checked?