I'd call UE to discuss your fit problem. With mine, there is no break of seal regardless of facial contortions (I, too, make strange faces while working out, which is what I primarily use the UE5cs for.) And there is a definite positive seal -- not quite as tight as foamies, let's say, but much tighter than with trad tips.
One thing you might want to discuss with UE is to have them paint more acrylic onto your existing phones. This has the effect of tightening the seal while keeping the same basic shape. On the other hand there might still have been a problem with your molds to begin with -- perhaps the length of time left for them to "cure" in your ears; the material used; the depth of insertion; and so on.
You should rest assured, however, that once you get the fit right it is very snug and tight-sealing, regardless of facial expressions! So there is defnitely something wrong with yours now, and it is well-worth fixing.