Bit of a random one.... and it's stumped me.

I'm just putting up the lights for my display this year, and can't get my WS2812b tape to work. It's 3 complete strips of 150 led tape (so 450 in total) all daisy chained with power injected where needed - run off an Arduino Mega 2560 connected to VixenLights.

Last year, everything worked perfectly with this exact setup - but this year I can't seem to get any control of them. Occasionally a few random individual LEDs will just be on in random colours (but static) - then I do a power cycle and everything could be on at full white - or random flashing through the full spectrum.

I just can't get my head around what to do next, and after a couple of days of trying to figure it out for myself - I figured it was time to try and get some help.

So just wondering if anyone else has had something similar happen - or if it's something really obvious that I'm missing. I'm a pro sound and lighting technician in theatre, so don't like to admit defeat with lighting... but I'm still a relative newbie to the DIY Christmas world and just can't get it working

Any bright ideas would be much appreciated!