Why do I have these weird strokes?

Well, you likely didn't produce a clean cutout in Photoshop/ didn't mask correctly and now the overlap edges have degenerate transparency due to leftover semi-transparent pixels. You need to clean up your stuff.

Mylenium

Impossible to know if you don't give us context and details. Here I leave you a link that can help you make your query in a better way.

FAQ: What information should I provide when asking a question on this forum?