Hard disagree. One should not go around making biological conclusions based on the fact that you see a "queue" shape. Different computational biologists diverge on whether such techniques are useful as visualization, but interpreting them in that way (i.e. a downstream analysis in the embedding space) is not the way to go. Many computational biologists, at the very least, caution against such interpretations.

Comparing t-SNE and UMAP, our experience is similar to what you have said: the latter is way too instable and it produces too many fake clusters. Unfortunately, the latter has been widely promoted on the net by so-called computational biologists.