I have a Raspberry Pi 2 Model B Rev 1.1 that was running ok from a 5v 2A power supply. It was running jessie.
I saw there is a recent new version of stretch 2018-10-09 so thought it was about time I downloaded it and installed it. Rpi boots and runs OK but now it has and undervoltage warning and a lightning symbol when powering up. The Pi still seems to work OK.
Just in case it was the power supply going duff I swapped it for another 5v 2A supply, but the Pi still gives the undervoltage message on boot up. Only a keyboard, mouse and screen are attached to the Pi 2B and I thought only a 1.8 amp was ok for this model.
Is this an error in the latest stretch version ?? The old jessie on the SD has now been overwritten so I cant check the Pi with the old but this did not happen before.