There's a visual/game bug on the boss stage of Stage 6 with regards to obelisks. Appears to happen on occasion when no deaths occur in the previous rounds but can be fixed by leaving and coming back in after dying.
The spider web on the obelisks may be invisible. Therefore, having all the obelisks cleared of the spider web visually may not stun the boss. However, it is possible to get lucky and explode a hoarver on an already cleared obelisks and this will lead to the boss getting stunned. Does not work on just any obelisks, likely only the one that is visually bugged.
NA PC server