Accessing 3 websites

I use IE11 & Firefox 52 with Windows 7 and access many websites.
I have 3 sites that are giving me intermittent access problems and they are all hosted the same server on Data1.
Model Rail Command
Your Model Railway
Platform1 Model Railway Community
I can access any of the 3 sites but as soon as I do so, any then attempt to go to another page or one of the other sites, it can’t be found - the system times out.
I have to wait for some time or reboot my PC to access a page on any of the 3 forums and then I am unable to access other pages, etc again .
So to prove to me it is not my PC ( but it maybe), I can then access any other site including the host UltraBB site.

I have cleared cache and done a System Restore to no avail. So I am at a loss to what to do next.
Any ideas please?

Would any recent Avast update done anything to my info on my PC about those 3 sites only?

Ron

https://forum.avast.com/index.php?topic=200429.0