What's the reason you're using Screen Space - Camera instead of Screen Space - Overlay? (It's fine to use Screen Space - Camera. But there may be additional configuration details to look into.)
Try disabling the Canvas Scaler. The UI probably won't look right, but that's fine for a test. Does the UI look similar in the editor's play mode and in builds, assuming the approximate same resolution?
Check the first scene listed in your project's build settings. If it has a Dialogue Manager, check its settings. If the first scene doesn't have a Dialogue Manager, check the second, and so on. In builds, the first Dialogue Manager to appear will survive scene changes and replace Dialogue Managers in subsequent scenes.
Oh gosh I feel really dumb now I forgot that I had put a manager on the main menu screen and that one didn't have the settings set properly! Thank you!!!