Yes, I've run into this as well. I have an Invoke connected to my PC at home, and another to my laptop at work. The home PC is always on, but the Invoke is always disconnected when I come back from more than a few hours away; oddly, whenever I turn the laptop on, my work Invoke connects automatically just fine.
However, both will disconnect at random times for no apparent reason; at work this can result in my laptop blaring my music embarrassingly loud. My laptop sits literally inches away from my work Invoke, and my PC sits no more than 3 feet away from my home Invoke.
If they could fix this issue, I'd have no other complains about the Invoke ever. I bought them knowing full-well that they'd never be an Echo, but rather as a high-quality bluetooth speaker. Alas.