Breach Enemy of Concealment hitting me from beyond the veil

Bug Report ID: #3,373,248,795

When running Breach encounters in a mirage, an It That Crawls of Concealment (magic monster) seems to have survived the closure of the breach that spawned it. For the entirety of the rest of the mirage, an invisible attacker followed me everywhere (and killed me once). It was untargetable and completely invisible, but mousing over its approximate location did show the health bar/name—which is why I knew what it was.