In my experience, when doing doubleweave on a rigid heddle loom, there is usually a shed (and usually it’s a down-heddle shed) that doesn’t completely clear when the heddle is put into position. Sometimes it’s a tension issue with a warp thread or two, but it can also happen when the warp threads stick to each other in the slots. The worst case scenario is you end up with floats, and floats can be fixed.
To mitigate this, I check the sheds to make sure they are clear every time I advance my warp. If the sheds are not clear, I identify which threads are problematic and then try the following:
Hopefully these tips for achieving a clean shed will help. Doubleweave can have a bit of a learning curve, but it is well worth the effort. It DOES get easier (and faster) with time and practice.