I assume its because if a broken vertex table. Under tools in 3dsmax there should be somewhere the vertex channel listener. Alternatively run this maxscript in the maxscript listener:ChannelInfo.dialog(); maybe it can give you some info on what might be wrong because I highly suspect a wrong table for the UV, smoothing or…
I`ve had some problems with the relax tool as well, but I think I found a solution to the problem. If that happens, usually I just select all the faces and choose "flatten mapping". Then I convert it into an editable poly and add an unwrap modifier again. After doing this, my "corrupt" meshes have worked just fine with…