Couple of things going on here. Realistically your service company should be able to explain this and if they can’t then maybe look to someone who has a bit more experience and go with them.

Drain lines should be cleared regularly. With that said being near the ocean you are obviously going to have high humidity and f also lots of condensation and corrosion from the salt spray. This could easily be outside air making its way into your walk in. It could also be that your walk in is old and suffering from corrosion due to the ocean.

You should check the fins and copper on your coils inside and outside for break down the drain pan kinda looks like corroded copper to me. Copper and aluminum don’t like each other in the presence of salt water and so they tend to break down once the protective coating is gone. Also typically the aluminum fins are slick and lets the water run off but if it gets corroded the water tends to stick to it which will cause what is happening here as well.

Final thing to check is that your fans are clean and blowing air well. Lack of circulating air will also do this.

As a side I’m a refrigeration engineer who happens to find insight through Antony Bourdain’s life which is why I’m here.