Can you post a screenshot showing the entire interface, before and after the issue?
Which dissolve, the blending mode?
What kind of images?
Please post the contents of Photoshop's Help>System Info... menu, so that we get to know your OS, its version, the exact version of Photoshop you are running, the date of the GPU driver, etc. If your post disappears, do not repost it, as it might need to be approved by a moderator. As an alternative you can save it to a .txt file on your computer and attach it on your answer via the forum. (attachments do not post from e-mail)