Martin....do you know the type of synthetic [plastic is a big group of many variants] parts supplied in the kit?........the first spraying attempt appears as th epaint too thick or too many coats too early
, the last attempt suggests static electricity dust attracted to the parts
or did you use double sided tape to hold the parts?......if so a possibility is the solvent fume in the paint has reacted with the tape & released a gas particles that have attached to the parts?
Get the bamboo kitchen Chopping board.......drill 50 x 1/16" diameter holes in random positions & blow out the dust ...spray board with IPA & let dry....try supporting the items on a bent Bobby pins.........These days, Methylated Spirit is grain based and ever after evaporation and condensation still contains a trace of synthetic oil
...so after a gentle washing in warm soapy water [kitchen dish washing detergent], then blow dry followed by an aerosol pump spray of 99.8% IPA.......then a warm burst from the family hair dryer...the parts elevated on the pins in the boards will assist with drying.....
Finally try the spraying in the bathroom....[tiles & low dust environment].....[maybe wait until Mrs Davis is at the shops
Derek