A V30 label doesn’t guarantee the camera will always be able to write reliably in real use. If your HERO10 says the card is too slow even though it’s V30, common causes are card corruption, formatting issues, compatibility problems, or outdated camera firmware.

The first thing to try is reformatting the microSD card in the GoPro. That often fixes file-system issues and was reported here to solve the problem. Also make sure the camera firmware is up to date.

If the error continues, try another known-good V30 card from a reputable brand. Cards can degrade over time, and a card that worked before may start causing recording stoppages later.

So in short: the message doesn’t always mean the printed speed rating is wrong—it can also mean the card or its formatting isn’t working properly with the camera at that moment.