In MS Word 2016 on MacOS (and potentially other versions), a bug occasionally crops up (sometimes following a Find and Replace action) in which ⌥→ (option right-arrow, "WordRight") moves the insertion point to the right-hand end of the current word (here| ), not the left-hand end of the next word ( |here). (However, ⌥← continues to work as expected.)

By accident I have found a workaround:

Split the screen (Window: Split, or ⌥⌘s), then drag the horizontal bar down to the bottom of the window (not up).

The cursoring now works as expected again.