Thank you to Michael B for letting us know about recent fixes to the Raspberry Pi kernel which affect RTL-SDR users. If you've been experiencing error "rtlsdr_read_reg failed with -7" when running RTL-SDR software on Raspberry Pi 4's running a Linux kernel with version 6.1 or higher, a Raspberry Pi kernel fix has been pushed by Pi Foundation which should fix the problem.

This problem "rtlsdr_read_reg failed with -7" appears to occur after having closed any program that uses an RTL-SDR, and then reopening it.

This doesn't seem to have been an issue for the older 5.12 and 4.19 kernels where this issue was previously fixed, but Raspberry Pi recently moved to the 6.1 kernel in May 2023 where the issue came back. Raspbian releases after this date may have been problematic.

The official Raspbian should eventually update, but if you've been experiencing this issue, you could try update your kernel now using:

sudo apt install rpi-update
sudo rpi-update

Alternatively according to Michael, kernel version 6.6.y should also have this problem fixed:

sudo rpi-update rpi-6.6.y

Note that updating the kernel could break other software, so doing this is at your own risk.