I've had an IHG account for years and have several million IHG points. I've never had any problems with anything.
I've always had my preference be IHG Points for all stays rather than Airline Miles. Last week, I was looking at my account and it had been changed from Points to Miles. I clicked on the detail and it showed an unfamiliar name and a United Airlines Frequent Flyer Account number. I thought it might be random, so I simply switched the preference back to Points. That worked for a week and I checked today and it had switched back again to Miles with the same name and United Airlines Account.
I called IHG Customer Service and was told he "had heard of this happening but not very often" He offered no explanation of what it could be. His "solution" was for me to use a different email account and change the PIN. Which I did.
I plan on watching my account closely over the coming weeks.