Just a wild guess, but I'm thinking bad power connection (corrosion). I had a nagging issue with my AP and I eventually solved it by re-crimping every connector (Hot AND Ground) in its path, and loosening then retightening every screw terminal. Marginal connections don't show up as low voltage unless they're under load, they'll pass full voltage until the amp draw increases -- so a voltmeter might not show the issue if you're testing with systems at rest, and a Voltmeter won't show a drop. As a practical matter, it's hard to reproduce the issue while watching a meter when the condition is transient and the only way to test is while under way.

First check you could use CorrosionX on every spade connection and work each one (pull it out partially then push it back in). If that doesn't work then it doesn't mean you don't have a problem. Re-crimp every one.