I would open up a new current account with a new provider. I recommend the Co-op and Nationwide. Move everything over to them - that way you can leave these unidentified amounts going in to HSBC. If someone is trying to access your account, they will get no joy; if they have made a mistake, the money is there for them. And HSBC don't deserve your custom.
I did wonder if someone repaying a neighbour for some 'lockdown shopping' has made a mistake.
The King is to resume some duties.