There have been quite a few issues with people installing the Mass markings in the ast, but it can be fixed. What I can suggest is deleting the markings you have installed including the markings.cfg in the main FH folder. Then once that is done, I then advise you install them again and it should take away the problem.
As said above, it's possible that the amount of Mass markings you are installing could be a little too much for your FH to handle. It also depends on how much you have installed to go with the game (example: Big maps). Try deleting any maps you don't sue that could be taking up a lot of space in FeralHeart and maybe do the following to decrease lag as it is also another reason that you could be crashing:
Go to FeralHeart\\Video and untick the water reflection box. Also, stay on the same tab, go to View Distance and slide it all the way down to 0.
I do hope you fix this issue. Sometimes things as little as lag could be causing the problem.