Do you have multiple bindings under the CRM site on your IIS?
that problem usually happens when someone apply the IFD and leave 2 binds, one for a internal crm alias and another for the external
CRM only supports 1 IIS binding
https://support.microsoft.com/kb/2502671?wa=wsignin1.0
If you don't find a second binding, maybe it was there before. removing only does not solve the problem, you need to recycle IIS or the CRM IIS pool
