In the game, there is an event in which SCP-106 traverses the grated hallway of the heavy containment zone.
During this event, it will be invisible, but its corrosion will not. It will however be visible when pursuing the player.

(On a similar note, when it is stunned by the Tesla Gate it will simply disappear while corrosion will appear on the floor. Isnt it supposed to be seen descending into the ground?)

Happened to me both in 1.3 and 1.3.1