I am using a trapdoor to access my underground home and placed it on a small island outside of Riften. Added a map marker and entered game to start testing. I have tried all sorts of things which appear to sometimes work correctly and other times cause ctd.

Fast travel to Riften, approach the door - this has caused ctd and then worked fine other times.
When approaching the door I have entered the home, run around and then exited again - sometimes ctd and other times not.
I got rid of the map marker and repeated above with the same results.
I moved the door to another spot and repeated above with the same results.

I do on the odd occasion get random crashes in game, but nothing as frequent as this!

Can anyone shed some light on this for me?