Searching several generated worlds in 1.13, I have not found a single dungeon. My searches have been extensive, in both surival and spectator modes. When I load the same seeds in 1.12.2 I have successfully found several dungeons and have found they have not generated in the same location on 1.13, including the latest snapshots. (as shown in the screenshots below - apologies for the dark images). Even if dungeon generation has changed and are not likely to generate in the exact same location, I have still been unable to successfully locate a dungeon anywhere after hours of searching.
Unfortunately, this is a big negative when it comes to my playing experience and feel I can't enjoy it as much until this is somehow resolved.