Electrical faults on starting

Been having a few strange things happen when staring the car. Most days when switching on the ignition the needles drop down off the gauge for a few seconds, they do come back and work normally, or sometimes they go right up and back again. Is this the ecu resetting? Its usually accompanied by a loud bong or the doors locking and a mix of either 'passenger airbag deactivated' or 'handbrake on' on the centre console. I get a range of all these things or sometimes just one of them. Sometimes the car starts fine without issues. Any ideas? Also not sure if related but the digital oil readout is generally on 1 bar or occasionally flashing empty although the oil is full. I am using fully synthetic oil. The car otherwise runs fine mechanically and is fully serviced. But does fail to start on few trys occasionally.