Hi

I can't be 100% sure but the symtoms you describe indicate a possible hardware problem with the electrical contact for the high E piezo pickup element to me.   I would slacken the high E string and then ensure that the pickup element is properly seated in its place in the bridge.  There's nothing to dismantle.  The pickup element will feel as if it has a little play in it and that's normal, but assuming the basic design of the pickup element is the same as with the older generation Variax guitars, then the metal of the bridge provides the electrical return path and it's important that the element has a good contact with the bridge.  Re-tighten the string and see whether the situation has improved or changed.

If that doesn't work, then the guitar may need to be checked over by an Authorised Service Centre and a replacement piezo pickup element may need to be fitted.

Nick