Unpopular pages with short titles, e.g. [[Sop]], [[Topo]], do not appear in the top 10 opensearch suggestions, so VE thinks the pages don't exist. However, they definitely do exist.
This, along with bug 50898, suggests that the VE team might need to implement its own wrapper web API for link suggestions.
Version: unspecified
Severity: enhancement
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=54361