The gurus have said on Twitter they are aware and investigating.
I have also have this issue and have reported it in Crin's bug thread but I thought I might expand a little here on what happened and how I recovered the game.
I had been playing very happily. The game runs well, I hadn't experienced any lag and the graphics are gorgeous. I had scuba dived, chatted to mermaids and even VISITED resorts all without major problems (a few irritations such as being returned to the water surface if the camera tilts up too far or being returned to land from a cave but nothing serious) I had been using just one save the entire time.
Then I decided I wanted to try resort OWNERSHIP. I created a sim in CAS and settled him into his empty lot with just his tent :) He had nothing in his inventory, no achievements, just a brand new sim. I then had him buy Hobarts (I think that's what it was called, I changed the name) Hideaway (the free one)via his phone. He went right on over to visit. We were able to wander around and go into buy/build and delete a few things, it was only once I interacted with the front desk that the freeze arrived. The game engine was running but I couldn't control ANYTHING so I task managed my way out of the game and reloaded.
Because my sim was already on the resort lot when the game loaded it froze almost immediately. I reloaded once more, same result. Worse still there wasn't a .backup file for IP. I thought I'd lost everything I'd ever done in Island Paradise.
The next time I loaded the game I hit pause as quickly as I could before the game froze and I switched to edit town. From there I evicted my sim from his home. I then replaced him back into the same home (Well, empty lot and tent that is!) and got him a job as a life guard immediately (so not one of the regular jobs but an open hours one) and then had him PURCHASE the same resort. (It was no longer free). He went on over to check out his purchase and has been running the resort successfully ever since. Now he only goes home to pay his bills so that the repo' man doesn't take his tent ;)
I also learned my lesson and now have multiple saves of my progress! Just in case!
I don't know, maybe something in there is relevant. See my post (page 43 of the bug thread) for my pictures of the weird sim I found outside the same resort. The 'sim' was actually multiple sims, with names of sims living in the IP town all moulded into one sim. VERY bizarre!
My game is mod/hack/cc free and always has been
Desktop: Win 7 64 bit, 16 Gb RAM, i7 processor 3.40 GHz, nVidia 580 GTX
