I had a similar problem. It seems to come from editing the models after already establishing the sequence. In my case I had two models, one which accessed the channels in a whole pixel strip, the other which referenced portions of the strip independently so I could have different effects on different sections. I wasn't using the model that accessed the whole pixel strip at once but the XML still had references to it anyway. Possibly because I changed it from the original sequence. I had to go into the XML file for the sequence and delete those manually and the problem disappeared.
I have had the same problem changing face models after the sequence. If you do them first, then do the sequence everything is good but when you change them after the sequence there seem to be "leftovers" which cause problems. XML isn't hard to understand, I have just taken to editing the XML file directly if I have problems and the cause is usually obvious.
