Greetings,
Have you tried adding an interchannel delay to your scan? Use the interchannel delay input to the AI Config VI to specify the waiting time between sampling channels within a scan. The default value for interchannel delay is -1.0, which tells the AI Config VI to use the channel clock rate LabVIEW selects. Adding an interchannel delay will give your multiplexer more time to settle before the 6115 acquires data.
Regards,
Justin Britten
Applications Engineer
National Instruments