calling execute() every tick

I don't think you should get 2 scans in one tick, but I did find oldwiki:DoubleScanning the other day, where David Alves said: "f you skip a turn before handling the ScannedRobotEvent for that turn, you'll get 2 ScannedRobotEvents on the next turn. You only miss lose events if you skip 2 or more turns in a row, if you miss one you'll just get extra events on the next turn."

My guess is that this is likely to have long ago been fixed, but I don't know for sure. It seems like Wompi and I have found some similar issues recently, so maybe something like that could be happening?

Having everything in onScannedRobot except a turnRadar in run() makes sense, but I thought you'd still need the turnRadar in a loop, wouldn't you? If you skip a turn and your radar slips, will it ever move again?

No, if the radar slips, I'm well and truly out of luck. Interestingly enough, my weird rounds (when I have battles slow enough to observe visually) seem to happen right from the word go.

might be worth exploring the idea of getting a non-onScannedRobot Universe update method, and put everything I can in run()?

Those rumble rounds (with about 6 bots on my rumble client, MN's and KID's it looks like) with completely zero score are concerning to me too.