could be number of things
laying in to quick and 1st coat hasnt set and is moving
spraying to much water i never use spray bottle seen blokes using them to much water for mutli
or even applying you plaster to thick
you have to work with the suction of the wall or ceiling there is no set time i like to put it on then clean my edges up then see if its ready for a trowel you now when its right when you trowel and it leaves no lines then 2nd coat it.
skimming on bonding has a higher suction than plasterboard...
im new to this site didnt even know it was here else i would of joined a while ago come across it when i was serching for this new plaster that doesnt need pva.
anyway i have been in the trade for 9 years since i left school