There may be a few different issues going on here-
Firstly Ensure you have input and output buffers, there is occasionally some issues with removing buffers from combiners.
Secondly you weren't very clear on what you use your Random.Uniform(1, 4) on. If this is how your calculating your priority on each entity, the issue may be that this distribution is returning real numbers (as opposed to integers) and the decimals differences invalidate your matching condition on your combiner.
You may want to Math. Floor, Math.Ceiling, Math.Round this distribution to ensure it gives you whole numbers.
Your best bet may be to build a simple model explaining what your trying to accomplish and post it here.