I have set up two Pi's, one as master and the other as a slave. I have the slave running off a USB power bank which the lights also run off (50 square pixels 5V) and have wired things up as per others have done with the ground of the pi and the ground of the power bank connected together. When I run a sequence, the lights running off the USB power bank and slave Pi are nicely in sync for about the the first 35 secs and then the sequence pauses and stutters for about four seconds and then goes back in sync. About 35 secs later that same thing happens. I have tried different effects in the same sections of the sequence in xlights but always happens in the same place (sequence runs fine on the computer monitor in xlights)Any ideas why this would be happening? I have the outputs all set to multi sync on the Pi's. The lights are connected to the Pi via one of SmartAlecs Pi pixels. Any thoughts appreciated.