I've added "castspriteshadow" to the powerups. For some reason the shadow appears but it isn't on the ground but is slightly above. I've attached a picture of a Soulsphere on a pedestal on map 02 of NRFTL so that it's easier to see.
I'm using the Vulkan renderer but it also happens with the other renderers. I have the latest release of GZDoom and I've also tried it on the latest DRD builds from the 17th and 18th April.
PS: It's hard to say for sure but it looks like all shadows hang above the ground including monsters.
Probably user error but thought I should share in case.