I can't reproduce so far. Do you see any errors in your browser console when this happens?

No errors, just warnings in the Google Chrome console and I made sure to check the console before and after I clicked Edit source and replicated the bug and nothing was added so the console log was there from loading the page. Note: all extensions removed except AdBlock which is disabled for en.wikipedia.org. Here it is

I can select the text where the source should be but I cannot see the text and markup.

[Removing BetaFeature tags since VisualEditor-MediaWiki-2017WikitextEditor looks appropriate]

@Waddie96 Please provide exact reproduction steps, such as the exact file page, the specific steps you took, your browser and browser version, operating system and operating system version, and anything else you think may be relevant. Thanks!

Steps to reproduce:

All beta features are on, logged in as Waddie96 on en-Wikipedia, no extensions installed on browser.

1. Goto https://en.wikipedia.org/wiki/AgriSA page
2. Click the logo (in this can it's this one: https://en.wikipedia.org/wiki/File:AgriSA_Logo_2018.png)
3. Click more details
4. Click edit source at the top tab

5. This happens, I see white where there should be source code.
   

6. As can be seen here, I can select the ghost text. So the text is there I just can't see it.
   

7. If I update the text somehow by clicking enter or another input key, then the text appears, like this
   

Software info:

macOS 10.13.4
Google Chrome Version 66.0.3359.117 (Official Build) (64-bit).

Wikitext syntax highlighting beta feature causes this. If you turn it off, there is no problem. @Waddie96: FYI.