I have noticing a certain happening with my Illustrator 24.3 on Mac OS High Sierra 10.13.1 on my iMac desktop computer. This sporatic thing happens where when I save an illustrator file with multiple layers, while I have the file open after hitting command S (I cannot use Save As because the files will not save that way, so now I use command S) the layers are just fine. But when I close the file and then open it again, some of the layers are condensed into an embedded rasterized image. I have tried restarting Illustrator with the shift, command, option keys held down, and I've tried restarting my computer. But for some reason I notice this occurence every once in a while. Is there a way to fix this?