Comment by SkyPuncher

I'm sure you've tried a bunch, so my comments might be talking into the void.

I had a similar issue that turned out to be a slightly loose battery connection. While the battery clamp was making contact with the battery terminal, I didn't tighten it enough and it made poor contact.

Is it correlated to temperature at all? If it is, I wouldn't be shocked if something, like a relay, is building up heat and increasing resistance to the point of operating incorrectly. A short nap might give that component enough time to cool off.