Failing bottom job cornflake nightmare

[I14]

I think 'Itdepends' was on the money. Have a look at the back of the blue flakes. I'll bet you'll find it's black ie failure has occurred between the old black bottom paint and the new black layer. Do you know what the original black bottom paint was? It must be very hard, perhaps a non-ablative 2-pack epoxy designed to be regularly srubbed like the old anti-fouling racing yachts used to use, and was not prepped (sanded) at all by the look of it. Unusual to have such poor intercoat adhesion but you've proved the point.
Remedy is to remove both new coats and wet sand then recoat with Micron 66 or similar

[jalmberg]

‘If you want something done right, do it yourself.’ — Noah

[David Johnson]

I have used Interlux CSC for many years, with a bottom coat contrasted with the finish coat to act as a signal. My impression from your story and pictures is some combination of inadequate prep, application when it was too cold (Interlux says 50 F but that is really pushing it, since the surface dries but underneath doesn't), or splashing too soon after application, which let's the partial-thickness dried paint slough off. Sanding to solid paint surface, cleaning with the proper prep potion and putting on new paint thin enough and in warm enough weather to thoroughly dry between coats and before splashing should take care of it.