Enemy Liliana 1 (Defiant Necromancer) used her first loyalty ability on me and instantly caused a soft lock. The cards I discarded were Talent of the Telepath and Blue Sun’s Zenith. Loop prevention system never kicked in.
In the last 2 weeks, I have actually experienced a lock for all 3 of Lili’s abilities. At level 2, it deals damage to plainswalker, then locks before dealing damage to my creatures. At level 3, it similarly locks after restoring the first creature.