Can someone help me understand why my bonded nylon thread keeps unwinding itself? Juki DDL-5550, noob

Your machine is not threaded correctly in the photo. After the thread goes through the tension plates (looks correct), it should go up over that "check spring" just above it, then down under the upside-down-"L" shaped chrome piece to the left of the tension plates, and then up to the take-up lever. That by itself can cause thread breakage at the needle because there isn't enough slack in the thread. Here's a diagram.

You're also skipping the thread guide at the top of the needle (hole in chrome piece), which is probably not related, but should be used.

See if that helps?

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