I have recently come up with two ui nodes that are both experiencing the same problem.
If you look at this picture, I have 19 linear-gauges in a group on the dashboard.
This picture shows none of the linear gauges showing up under the Tank Temperatures group.
I then added the ui_list node @nisiyama to see if it would produce the same result, and it did not.
Running a diff on my code and the ui_list code doesn't produce any blatant differences.
Does anyone have an idea of what could be causing this?