Thank you very much for the replies and your work :).
Could you explain a little more what you mean by "layers bound to the player or an event"? Does that mean layers loaded on entering a new map won't be displayed, in general?
Viewing post in Minimap for RPG Maker MV & MZ comments
GALV Layers lets you choose a "character" to bind a layer, that is either the player or an event. When you leave it empty the layer sticks with the map.
Right now, the minimap supports only static layers that are bound to the player or an event, so I suggest making an invisible event where your layer should be. I'm already planning to support static layers that are not bound to a character, too, so you can also wait a few days until I release the next update.