After upgrading to iOS18, safari can't resolve /api route in my website

I'm one of the developers of a medium size website, which runs angular 18 frontend, and a .net openApi backend. The site is served through iis with the api as a web-app accessed through /api with help of url-rewrite-module.

After upgrading to iOS18, safari is unable to resolve myurl.com/api or any of it's route. The frontend located at myurl.com also sometimes has problem loading. By pressing update-symbol/force reloading the site sometimes loads the frontend. But the wierd part is that the api isn't accessable, neither directly from the website, or by navigating to simple /get routes in url.

Edit: Seems like i can resolve routes that returns image/png, but not data like text/json

This issue is only related to safari on ios18. It works perfectly on ios17 + safari, ios18 + chrome. I have tried on multiple iPhones running ios18 and it's the same issue there.

Is there something im missing about new safari 18 for ios? Haven't been able to locate other developers with similar issues.