I recently got a Vox Tonelab EX, and ever since I've started using it I've noticed a problem. About 25% of the time, I will turn on the pedal, and it will sound amazing. I love it. But 75% of the time, I turn it on, and the sound is either muffled, like it is trying to push through a wall, or fine until it gets loud, and then it cuts out.

I made a video demonstrating the problem. For those of you that are familiar with the pedal, yes, I am using the pedal's built in speakers for the demonstration, but the same problem still occurs when using the line out. If you skip to the last 20 seconds, I set the pedal to clean and turn it up a little, and you can really hear the issue.

Here's the video: https://www.youtube.com/watch?v=wnvxD5aHQfo&feature=youtu.be

Again, sometimes the pedal works. I don't know why or how, but it does. Sometimes, when it's working, moving it can cause it to revert to the state that it's in in the video. I'm no expert, but I opened it up to check for loose connections and there was nothing blatantly obvious. But as I said, I'm no expert and I'm probably not looking in the right places. Any suggestions?
Did you ever get this figured out? I have the exact same problem. I've switched out all of the cables to ensure that's not the problem. I can be playing for 10-15 minutes and it will sound just fine, but then it will just randomly crap out like it's lost 70% of it's power/effects or something. It's almost identical to what your video showed. Very frustrating because I do love how it sounds when it actually works. I just can't count on this thing to work consistently. It does this 90% of the time.
I too have the same problem, sound goes off for no reason and then comes back, cant trust it on stage. Recently the tuner also got stuck