Hi @bjmackay ,
I would love to assist you with this. Do the same thing happens when you charge the phone using a charging plug connected to the mains?
Could you please run this test and let us know the results? Head into the Samsung Members app> Support> Under Diagnostics tap View tests> Cable charging.
Thanks for giving this a try @bjmackay . How long have you been experiencing this issue? May I ask what charger plug and cable are you using?
Would you be able to place the phone in Safe Mode and test if the same thing happens? You can find how to do this here: https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/