LOS Issue; wall artifact?

[Tabarkus]

I am having an intermittent LOS issue that I can't figure out the cause. The issue began with a player's token disappearing from the map upon movement approval with token lock on. A shadow shape is created on the map at times that acts as if it is a wall when the tokens are moved. It stops light, player vision, and token movement unless the GM holds shift and drags token. This effects all the player's tokens. The shapes and locations of these invisible walls have changed as I've fiddled with things trying to resolve the problem.

Shadow artifact.png
Shadow artifact occluders.png

Ruleset 5e, running Dungeon of the Mad Mage, level 18 map.

If I turn off LOS the shadow persists but the token can move through it. If I turn off lighting the shadow and movement restriction persist.
The artifact persists even with a FG restart. I removed all the extensions I was using and it still persists. Removing the character's token from the map and then the character from the combat tracker and replacing her didn't help. I removed token light effects with no changes.

I copied the map, placed the character tokens and the issue resolved. When returned to the original map the problem persists.

[Zacchaeus]

The only thing I can think of is that somewhere along the line you've added a mask to the map possibly. Try going into the mask tool and if it's lit up click on Remove Global Mask

[Tabarkus]

Thanks for the thought Zacchaeus. It wasn't a mask but your suggestion did make me think of other layers and so it was an object causing the problem.