There is an issue when using TwoColConflict together with the new Wikitext editor. Both extensions are available as beat-features on beta, so the issue can be reproduced there by enabling both beta-features and going through a normal conflict resolution.
When a conflict occurs, a dialog is shown:
After clicking "resolve conflict" the TwoColConflict resolution-screen is shown including a new icon to switch back to visual editing:
After clicking the new icon, another dialog asks you again if you really want to switch back to visual editing (everything is fine until here):
Only after confirming the switch, the visual Wikitext editor loads again and the page is screwed up: