Poor drops of what exactly, if I may ask? The Oxas now drop 2-3 portal ores at each collection! If yours doesn't, force close and restart your game and if that doesn't fix it, definitely contact support!
If you mean they don't spawn the Portalpillar Gigantus every time, yeah, that's true, unfortunately.
The only bright side is that the Portal is only 2 gems to speed up to be able to spawn a new Portalpillar Gigantus.
ETA: Sorry, just saw your edit. You did mean the spawn. Yeah, I know, that's still very random...