Explorer freezing halfway through copying happens all the time for me, usually it means Windows' I/O buffer is full and the drive is taking its sweet time actually doing data transfers. Windows will happily show you gigabytes per second being copied to a USB 2.0 drive if your RAM is empty enough, but it'll hang when it tries to flush.
Sometimes it's interference, sometimes the backing SSD is just a lot slower than it says on the box. I've also seen large file transfers (hundreds of gigabytes) expose bad RAM as caches would get filled and cleared over and over again.
You should be able to go into the Windows settings and reduce the drive cache. Copying will be slower, but behaviour will be more predictable.
Sometimes it's interference, sometimes the backing SSD is just a lot slower than it says on the box. I've also seen large file transfers (hundreds of gigabytes) expose bad RAM as caches would get filled and cleared over and over again.
You should be able to go into the Windows settings and reduce the drive cache. Copying will be slower, but behaviour will be more predictable.