Graphics replaced with black ticks

Hi everyone, first time posting here, but I am a very long-term user of Clickteam products.

Today I have come across a problem that I have no idea 1.) how it occured, or 2.) how to fix it...

I have been working on a fairly large-scale project for a long period of time now, and coming extremely close to the end of it, however, randomly, some of my active objects have been cleared of all images, and have been replaced with white squares in the animation editor... They are invisible in the actual frame editor, and during runtime, whenever one of these images is supposed to appear, it is replaced with a little black tick, that acts exactly how the original sprite should have (movement, transparency changes, etc)...

I have no idea why this has happened, and the three backup copies have had the exact same problem happen to them too... Other games/projects/files appear uncorrupted. I also tried reinstalling, which did not solve the issue. Any help would be very much appreciated.

Edit - Update: I went to start replacing some of the images, but it kept saying "must contain at least one non-transparent image" - even though the image is clearly there... Cloning frames doesn't work either.