RG750GL don't answerign and relaying big packets

I have a few RB750GL. With some of them there is a problem with big packets. For instance - don’t answering to big PING packets (65000). But other - responses. Where is the problem? Why some of them don’t ansewring and don’t relaying big packets?? There are big problems with network applications and other network services that works across that failed RB750GL.

No one have that problems with that board? I don’t believe. We have bought new one (RB750GL)- with THE SAME PROBLEM!