I found the SD card (128gb) had stopped being detected, and the camera was showing no card insterted. I tried pwering the camero on and off to no effect and then tried removing and reinserting the card it which seemed to allow it to be detected and work again, but soon after it stopped being detected again, and could not get it to be detected like before.

I removed the card and using an adaptor viewed it on my laptop. The laptop showed it was full but I could play back a lot of the videos. A great many videos had xxxxx. at the beginning of the file name and wouldn't play back - perhaps they were corrupted. As the card wasn't being recognised I had nothing to lose so deleted the xxxxx videos. I then reinserted the card back into the camera and it started working. It seems being full made the card unrecognisable.

Although the camera is set to loop recording, I got the impression that when the card became full, the camera did not record over the top of older recordings (or perhaps did and corrupted them, I've no idea) but instead failed to recognise the card. Deleting files so the card was no longer full seemed to make the card recognisable and usable again, and I'm guessing reformatting the card might work too, but the card would have to be recognised by the camera. I did format the card in the camera and it has continued to work fine ever since. I'm not sure if using a laptop/PC to format the card would work, but using one to delete files might and then reformat the card in the camera if it's then recognised might.

It seemed to work for me, so I hope this might help Tapo find and fix this apparently common fault (Google brought up a few of the same issues), or at least help some that have had the problem and be able to fix it themselves. It does require a laptop and a SD to USB card adaptor though (cheap on a well know auction site).