Run the check
Press and release the affected key once in the keyboard test.
Record whether keyup arrives and whether repeat events continue.
Compare the same key in a plain text editor and another connection.
Read the result
A missing keyup in multiple environments differs from an app continuing an action.
Limits and next step
A browser can miss focus changes and cannot see the switch contact directly.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.