What is causing "Loading.LoadFileHeaders" to take too much time when entering play mode?

Hi, in my project entering play mode takes over 1 minute and when I profile the editor I can see "Loading.LoadFileHeaders" takes too much time in the profiler but I can't see which objects are causing this. I tried selectively delete objects in the scene which are using animators, which are using navmesh agent etc. and tried to delete resources folder, plugins, editor scripts and delete all the scripts but it always takes over 1 minute to enter the play mode. How can I figure out what is causing this? Any help would be greatly appreciated, thanks in advance.