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I think there is a little visual bug when selecting multiple layers with SHIFT on the left side of the timeline (at least on Windows, I will check on Mac later). When I select the first desired layer, and then SHIFT-CLICK the last one, I only see those two layers highlighted, and everything in the middle not. But if I copy/paste them or manipulate in any other manner, I actually see that it did select all the layers, it just didn't show it. Scrolling the timeline up and down to hide and reveal again the selected layers does "unmask" the selection highlight though...

I've just tested on Mac and I have almost the same issue. For instance, if I have 5 layers and I select layers from 5 to 4, then I click on layer 1, it will select only 3 layers and not all of them.

Just to confirm - I've tested on my Mac now - exactly same problem - selected layers are not displayed highlighted unless I scroll the timeline or do something else with them.

I reported this some time ago and was talked out of it. Glad to see it confirmed.