This is exposing a pre-existing bug in mobile VE or MobileFrontend's VE integration or something in this ecosystem: you cannot initialize targets into a container that isn't already attached to the DOM. Previously, you could do this and various things regarding measurements would just break and render wrong, but now we throw an exception.

@Juliusz: Looks like the .surface element selector here is either not finding anything at all or it is referring to something that is still detached at that point:

https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/c4264d76bc817df71c6b3631afb19be737246c52/javascripts/modules/editor/VisualEditorOverlay.js#L16

It doesn't have to be fully initialised, but the target container element should however be somewhere in the document.

Change 110498 had a related patch set uploaded by JGonera:
Fix VE error with latest VE master

https://gerrit.wikimedia.org/r/110498

Change 110498 merged by jenkins-bot:
Fix VE error with latest VE master

https://gerrit.wikimedia.org/r/110498