Change 281456 had a related patch set uploaded (by DLynch):
Give the active link annotation inline-block

https://gerrit.wikimedia.org/r/281456

On examination, we think this is due to https://bugs.chromium.org/p/chromium/issues/detail?id=618318 , which also affects Safari (but not Firefox).

Change 281456 abandoned by DLynch:
Give the active link annotation inline-block

Reason:
This fixes some cases, but makes others worse. Investigation with David Chan confirmed that this is arguably a WebKit browser bug (with Firefox having a similar-but-different one), and browser tickets have been created.

If we assume browsers won't fix it, we could perhaps approach this in the linear key handler, checking whether the selection hasn't changed when we think it should. (This is, of course, fragile. "Should the selection have changed?" is a complicated question, and we abdicate it to the browsers for a reason.)

https://gerrit.wikimedia.org/r/281456

I just encountered this bug whilst editing https://wikimania.wikimedia.org/wiki/Travel_guide#By_plane (in the long list of links to cities)

I made a test case page at https://www.mediawiki.org/w/index.php?title=User:Quiddity/sandbox&oldid=3083245&veaction=edit where you can reliably reproduce it by:

• place your cursor anywhere in the word "test"
• tap left-arrow until cursor is at the start of the paragraph
• tap down-arrow 2 times.
• only the first tap will work

Then I found this bug whilst starting to file a task. :-)
Notes in case useful.
Also upstream seems to be stalled and could maybe use a hint or nudge?