SF2 has now started CTD when I delete Waypoints in Single Mission Editor

[TempestII]

Hello gents,

My full SF2 install has suddenly (circa a month or so ago) started crashing to desktop whenever I delete a waypoint in Single Mission Editor.  I've also noticed that it crashes more commonly on start-up, but after a couple of attempts, it'll launch to the Main Menu Screen.  However, if I delete a Single Mission Waypoint then it'll crash.  

I've moved my modded folders to an external HDD and re-installed SF2E and the Exp Packs and yet the crashes still occur.  Any help would be massively appreciated.

The only hardware upgrade I've done to my PC recently was to upgrade my GPU from a 980TI to a 1080TI; it definitely worked fine when I first did this but I have read the Nvidia thread on here that some users have had problems with recent software updates (I've made sure that my Effects aren't on "Unlimited" although none of the issues I've read in that thread seem to match what my issue is).  I did a search but couldn't find any similar CTDs either so I'm rather stumped.

PC specs are in my sig if that helps.  Thanks in advance.