Why are all my PNGs across multiple files suddenly appearing with white backgrounds?

Is there a system-wide Adobe glitch or system issue that has happened in the last 24-hours?  I have been using illustrator (and other Adobe programs) for over 10 years, therefore, I am 99.99% certain this is NOT something that I've done, it is an adobe issue.

Two days ago, my work (3 seperately saved files) were all fine; I have a number of  drawings/sketches saved as PNGs (just the vector line work) which are 'collaged' over A1 artboards to create a series of panels with my work.  I've opened all 3 files, and suddenly all the PNGs have white backgrounds so are therefore all blocking eachother. HOWEVER, the white backgrounds are only showing when the PNG is on the actual ARTBOARD, when I slide the PNG off to the side (where it's the grey space), there's no white background. What is happening here, Adobe? 

Unless this is something I have done (very unlikely), can you please sort this out ASAP, otherwise you should issuing every single person across the world a subscription credit for your system stuff-up.