It means the same. may contain can be used for sharing lines, sharing equipment at end of line, and of course mean that milk may be in the food.
Both comments man that the manufacturer is not sure that his food may on rare occasion contain an allergen.
There are of course higher risk foods than others, and yes some food producers over use the label when there is not a true risk.
we avoid not suitable comments the same as may contain.

my son is not allergic to milk, one of his allergies is nuts, so of course we avoid some chocolate, cereal and biscuits, because the may contain and not suitable label mean a lump of nut.

we are cautious but sensible when we check food labels.

If a product labels 'not suitable for milk allergy suffers' it means it was produced on shared equipment and the chance of the product coming in contact with that particular allergens is very high so it is best to avoid the product as a whole. The 'may contain' to to me is a catch all to avoid liability for any possible claims. This means that even though nuts or milk aren’t deliberately added to the food as an ingredient, the manufacturer can’t be sure that on some occasions the product doesn’t accidentally contain small amounts of them.

yes. same as. In EU label warning must be added with good reason. but this is still a grey area legally.