I would use parchment paper instead of foil. Maybe there's some reaction between the acid and foil in the brand of foil you use. Some foil is coated for various reasons. Like non stick coatings. https://www.google.com/patents/US6544658

So, with the multitude of choices of 'foil' available today. We might need to more specific for recipes.
Because a "non stick" foil might not..have the cooking profile in high heat as what most recipes would suggest as 'foil'.

Until recipe author chimes in, here are a few ideas.
Nor have I made that specific recipe, but yes have cooked with citrus.
Most pith (white layer between outer skin and inner fleshy fruit) has bitter taste.
Maybe next time, save the lime slices for garnish after baking & use one of these combo for lime flavor during baking:
1) use only lime juice while baking
2) use lime juice and lime supremes (the fleshy segments without white pith or inner membranes. fussy to cut, but sometimes worth it).
3) use combination of lime juice & zest.

I haven't made the recipe you're referring to, but this thread on a similar topic might have some relevant tips for you: https://food52.com/hotline/27896-how-do-i-get-rid-of-the-bitterness-in-my-fish-cake-mixture