As long as you can find a way to attack from far enough away, usually by throwing something, it won't enter combat - it is, indeed, systemic and replicatable (and remains so as of the latest patch).
Rather than fix the issue in their base engine, Larian performed a cludge fix, as they more or less always do; all enemies all have an unlimited self-heal skill now (compete with animation), which they spam out of combat as long as they're not at full hp.
