I am using a 6 button switch link to control pendants which have incandescent bulbs in them. Altogether total watts = 360. Every 5-10 minutes there is a single flicker. I changed out the SL. The issue remains. How can I diagnose this issue?

with incandescent lamps that sounds like a loose connection. 

1 hour ago, PapaBear said:

How can I diagnose this issue?

Step 1, put in a standard old-fashioned switch, or wire power to the load wire with a wirenut bypassing the switch.  Does the flickering continue?

Thanks for the tip MrBill. I bypassed the switch and there is no longer a flicker. Now what?

1 hour ago, PapaBear said:

Thanks for the tip MrBill. I bypassed the switch and there is no longer a flicker. Now what?

so the flicker is defiantly caused by the switchlinc then, tbh I had my doubts.  I've seen it plenty with LED bulbs but have no experience with it occurring while using incandescent.

I just saw this thread and thought I would respond with my experience. I've had two 6-button Switch Link switches exhibit this behavior in the past year, both after having worked fine for years. In both cases I replaced the capacitors in the power supply section with new caps ordered from Digi-Key and that fixed the problem. If you're handy with a soldering iron that may be the solution.