Hello,
On the basis of the new information, it seems likely that the problem is nothing to do with the normal operation of either unit (sending and receiving) or of the connection (cable). The midi link seems OK.
I'd be wondering about settings within the sampler. On the basis of what you say, the sampler does not seem to like sustained notes. You need to check the manual, and any settings that you can configure, to see if there's a maximum note length. Such a thing could be considered a 'protection' against the problem of a note/sound being left 'on' accidentally.
You said in your fist message that it wasn't a polyphony matter? The fact that you checked this suggests that you were wondering about such things. Of course, one of the reasons why the unit might cut off a long note IS to protect polyphony. Depending on the sample, the envelope, etc, you could have a long 'sound' playing that continues to use (waste) system resources even though no audible sound is apparent.
Why and how did you determine that polyphony was NOT a possible problem?
Maybe there is a setting - something like - Maximum Note length?
How long are the notes that are being cut off? How long are they cut off at? Do other notes (normal length) playing at the same time, also get cut off?
Oh, it seems less likely, but it's not impossible that the Sequencer may have a setting (for similar reasons) that is causing the problem. So check settings on that too.
Geoff