some acrylics do not bond well with plastic like vallejo , humbrol or any water based paint.
I try to use gunze or tamiya.
Gunze are the best as some tamiya matt paints do not adhere well, pick up grease from finger prints and will scratch very easily
Sadly gunze is now rarer than rocking horse s##t and sadly is no longer available in hannants or TAHS (or most places in the UK for that matter).
Tamiya is still good, but what's the problem with IJN grey and Light grey?
They practically dry as soon as it hits the plastic and dries very patchy with a very matt finish - and flakes off as soon as you touch it !
I thin my paints with isopropyl alcohol and some water ( dilute to taste),