YubiKey stuck in "busy" when using gpg

[dagheyman]

From @TomAtYubico:

When using other features such as OpenPGP there is a message stating that the YubiKey is busy which is correct. In this example below, I quit gpg and removed the YubiKey. Upon re-insert
the YubiKey Manager still reports that the YubiKey is busy.

To be sure that GPG is not running I opened the task manager, killed all GPG processes. Removed and re-inserted the YubiKey. The interface is still locked with the message YubiKey busy.

The only way to "unlock it" it is to restart the YubiKey Manager.

(Windows)