Obviously the paint you (yard) used is incompatible with what was on the hull before, and is not adhering to it.
You said it was 'same paint' but was it exactly the same? Maybe same brand, but different type? Some paints can require a primer to be used, depending on compatibility with what is already there.
To me the most likely scenario is a misunderstanding of exactly which particular type of Interlux was used previously, thinking the new paint is the same when in fact is is not. If there are old records/invoices then this might be able to be checked.
Of course it is possible that the paint formulation was off spec. for the batch you used. But that it pretty unlikely.
How was the prep done? Was the previous paint completely removed back to gelcoat? If so did anyone put anything on the hull (such as polish) before the paint?
Going back to gelcoat is generally not required if you are certain that the new paint is exactly the same (or labelled as compatible) with the previous paint. But if doing this it is good practice to prime any bare gelcoat. I have used Primocon to do this.
Could there have been any coating put over the previous paint? A while back there was a thread on using ArmorAll, or silicone based products. If that has been done then nothing is going to adhere to it!
The paint will likely need to be removed by soda blasting. If you do that, then use the opportunity to put a number of epoxy barrier coats onto the hull and then go from there with a quality paint.