Hi Forum Peeps!
I'm running into this SAME issue and it is incredibly frustrating. I have a Win10 i7 8GB Ram PC that is ONLY running myDMX 2.1 connected via USB.
I set the lights for an hour long show with very specific timings to the music timing. Literally timed to the second.
After I set all the lights, timings, hold and fade times, then save and turn off computer. When I return to the myDMX software the next day the timings are completely off...always faster than when I was using them before.
Also, the software doesn't seem to keep time at all with the video. Meaning, for every 30 seconds in a video the myDMX software will count 25 seconds...so, it's slower than the real-time video.
I have about 100 lights (individual dip-switch numbers) and am running 60 simple white dimmer pack lights and various LEDs such as Chauvet colorstrip, Rogue R1 Moving head spots, COB Cannon Wash lights, and ADJ 64 LED Pros.
I've tried the setup on three computers and the lag is prevalent with each.
PLEASE let me know of a solution.
I'm running the latest version (Feb 2017) of myDMX 2.1.