Why is my WLED constantly losing sync after I build it?

I ran into almost exactly this on a build where the strip wiring had to flex every time the lamp arm moved. Nine times out of ten it's not the soldering itself, it's the wire right next to the joint. Solder wicks into the strands and makes them stiff, so every little flex works that spot back and forth til a strand or two lets go. It'll still pass a visual check and even a gentle tug test, but vibration kills it fast. The fix is strain relief right at every connection point. I use a dab of hot glue over the joint plus a small zip tie a centimeter or two down the wire so the flex happens in the soft wire, not at the solder.

The other big one is slack. If the wires are routed tight thru the frame, any movement pulls directly on the joints. Give each joint a little service loop, like a coil of spare wire, so the structure can shift without tugging the connection. And if you used solid core wire anywhere, swap it out for stranded. Solid core is a nightmare in anything that moves.

For the data line specifically, keep it short and away from the power wires where you can. If it's running parallel to the power feed through the frame, the vibration can expose any marginal connection that was allready marginal. A small resistor right at the data input of the first LED helps keep the signal stable too, if you don't have one already. Also worth checking the connector side rather than the solder side. If you've got any JST plugs or a screw terminal between the controller and the strip, those are way more vibration sensitive than soldered joints. Pin headers expecially will work loose over time. Soldering straight through and gluing the joint fixed my random blinking for good. Last thing, if the base itself shifts on the shelf, some thin rubber pads under it will cut most of the movement before it ever reaches the wiring.

I had a similar situation when integrating a longer run of WS2812B LEDs into a non-rigid casing and found that the issue, which initially appeared mechanical, was frequently electrical noise coupled with the subtle movement. When the wiring shifts, it can introduce momentary ground loops or signal spikes if the data line runs close to high current power rails, making the system think it's receiving invalid data, thus triggering the blinking error. Have you considered separating the data line entirely from the power feed, perhaps routing it through a dedicated, shielded conduit if the structural limitations allow it? Even minute electrical fluctuations can mimic a severed connection in those sensitive protocols!

One thing that fixed a similar flickering issue on my build was the controller itself. I had the board just sitting loose in the base and every bump moved the whole thing, which was enough to glitch the data pin even with solid wiring. Screwed it down to a scrap of wood with rubber washers and the random blinkouts stopped almost entirely. Also worth pressing the LED strip flat against the plastic with some adhesive backing or clips so the strip itself isn't flexing when the frame moves. Does your strip run through any tight corners in the frame? Those bend points were where mine acted up first.

Before you start re-soldering everthing, find the actual break. I do prop repairs for a living and this trick has never failed me: put a multimeter in continuity mode across the data line end to end, then flex the frame slowly and watch the meter. The beep will drop out the second the cracked strand separates, and you'll know exactly which section is the problem. Found a hairline break inside a printed channel that way last month in under ten minutes after two days of guessing.

Also run the same test on the ground return. People chase the data wire and forget the ground path through a plastic frame has zero backup, one dodgy ground joint and you get exactly the random rainbow soup you're describing.

Old habit from my repair bench days: before I solder anything that might flex, I hook and twist the wires togehter first so the copper itself carries the load, not the solder. Even if the solder cracks you still got a decent mechanical joint. Learned that fixing marquee lights where the wiring got yanked around for years. Also, the adhesive backing on strip never sticks to 3D printed plastic worth a darn, it'll creep loose and the pads lift. A few dabs of silicone or little printed clips hold it way better than the factory tape ever did.