Sorry, I didn't realize I was being so inconsiderate, let me try again.
I don't know what the problem is, but if its LOD not unloading in the active cells, it probably isn't the only problem since whats on the screenshot doesn't look like a LOD texture but like some sort of yellow gradient texture. I've generated terrain LOD on my own, this happened, I deleted the LOD files and tried again, this time with the Viva New Vegas LOD guide as reference, to see if I made a mistake the first time but no - same result). These are the settings I've used and here is the fnvlodgen file.
Thanks for the help.