I’ve posted here both about multiroom playback working well after the upgrade to V3 and about it not working reliably. Having experimented a bit, I think I better understand what works and what doesn’t, so I thought I would post again since this might be of use or interest to others.
I have three devices running volumio on Pi’s – call them A, B and F. F is the device which is farthest from the wifi router. If I’m on device A or device B and add device F to the playback group, everything is great. Playback starts right away on both devices and is completely in sync. If, on the other hand, I’m on device F and add A or B, playback is slow to start and, when it starts, the music comes in very short bursts (less than a second each) with long pauses in between. Everything is indeed in sync but not exactly in an enjoyable way 
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So it really matters which device I choose as `group leader’. At a practical level, obviously, this doesn’t matter at all – if I want to do playback in two or three rooms, I just need to to choose A or B as group leader rather than F. So it’s only an intellectual puzzle. I do find it puzzling, though – even though F is farther from the wifi router than the other two devices, the distance poses no difficulty for other kinds of network traffic. It’s easy to see that synced playback would impose heavy demands on a home network, but it’s harder (for me) to see why the directionality would matter – whether the data flows initially from B to F (good) or from F to B (bad). Mostly, though, I’m glad to be able to enjoy the experience and especially glad that it also works for CD playback.