Some may have been removed due to the original owner leaving the site, Also if they have improper gender tags, Go against the T.O.S and such . MM can shed more light but my guess is if they were yours and they are gone its most likely due to them being improperly gender tagged. I would try re-uploading the ones that are gone making sure you tag them properly and such.
No, I see what you mean. There is a physical placeholder for the images in question and you can still see loves on them. But when you click the image you get the message
"This image no longer exists. I mean, it happens, ya know?"
If the image were deleted there would be nothing there to click on. I've reported this to Messmaster for him to look at. Don't delete the ones in question just yet so he can see them, but go ahead and try and re-upload the ones you're missing.
There was a bug where if you clicked a link to make a pic your profile pic, it would delete the original picture out of your gallery. I've fixed it and am monitoring. Thanks Potatoman for bringing this to my attention.