I know you said the battery tested as good, but a 10 year old battery has to be on its last leg. MINI's do strange & wonky things when the battery is going south. That's all I've got.
I have had something like that happen after a fill up on the way to MOTD a few years back.
I stopped and shut the car off and restarted and "limp Mode" was gone. At my stop I scanned the codes, cleared them and reset all the "adaptives" with my BavTech tool and kept going down the road.
