unable to toggle visibility of a text object on the map

[wmve]

STEPS TO REPRODUCE

1. start world
2. select text label
3. toggle visibility

expected behaviour: text becomes visible (toggles visibility state)
actual behaviour: text does NOT becomes visible; console warning generated (see below)

VERSIONS

DETAILS
a week after converting world to 0.8.6 and using it for much prep and one a play session, i discovered during play time that these green text labels i have placed in one room could no longer be made visible. since then i have determined that enabling furnace reproduces this issue. the following is a sample of the one of these text objects (selected). this happened for all the text objects i tested in that room.

here's the config of that particular text object:

every time i click on the button to toggle visibility the following message is produced (the counter increases) in the console

DATA
i am attaching an export of the scene.
fvtt-Scene-portal-chambers-1.210608.zip

[wmve]

i also missed the readme.... duh... ok.