Our customers have been complaining that they are unable to signin while checking out. They go into an endless loop of logins and their shopping cart empties itself. The only way to solve this is by emptying the cache. Our site museumreplicas.com displays this behavior but the sister site atlantacutlery.com doesn't. Both run on ML 7.1 and have similar modifications done on them.
It seems like something is going on in the signin process (which has not been modified)
Appreciate your support.