Side toolbar not loading in publicly shared View only board

This is not impacting me in any way, but my inner-nerd is curious as to why this is happening.

Someone has shared a board publicly in View only mode. When I load this board (both while signed into a Miro account or from a private/incognito browser window), I can see the side/vertical toolbar, but I cannot see it in my similar test.

The board where I can see the side toolbar:

My test board - https://miro.com/app/board/o9J_kmByH5Y=/ :

I mean, it starts to load, but then disappears:

Has anyone seen this before? Any ideas as to what condition(s) may be causing this? All I can think of is that I this board is perhaps using a different codebase.