Enemies spawn out-of-bounds on Lua Defense, turning it into "mission impossible"

[Graavarg]

• Has happened occasionally for a (very) long time, but unclear how it could be intentionally reproduced. Happens in both standard and Steel Path Lua Defense (this time in SP).
• Conclusively related to the spawning of enemies. Theory: due to happening "randomly"/occasionally the problem might be caused by ability/weapon effects affecting enemies during/immediately after spawn (pushing them "through" the tileset into unreachable areas, or something equivalent?).
• Squad: 4 Tenno PUG squad (not hosting), problem affected all players (unkillable enemy stops defense mission from progressing to next enemy wave), everyone had to abort the mission.
• Image included (enemy unreachable: outside and clearly below playable area). Can also happen in other places (= not the only "spot" on Lua Defense where enemies can become unreachable & "missions-stoppers").
• Has happened occasionally for as long as I have been playing, can occasionally be "fixed" in-mission by killing unreachable enemy with "far-reaching" Tenno abilities (depends on which warframes are present in mission).