Problem: After the latest Adobe Illustrator update, I noticed that my guides were disappearing when I moved them and would only reappear when I dropped them. This is extremely frustrating.
Solution: Disable Real-Time Drawing and Editing when viewing the interface on the GPU if you are running an older machine like I am. iMac (Retina 5K, 27-inch, Late 2015) running an AMD Radeon R9 M390 2GB.
I'm posting this up because I couldn't find any information on this on the forums and I'm very low tech savvy, so I just had to check and uncheck boxes in the program until I found the solution, hope this helps!