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A single keyboard key is registered, but no longer prints its corresponding symbol

I have encountered a strange issue a few months ago. From one day to another, the key for the following symbols no longer works: < > |.

At first, I thought this might be a hardware issue, but after using a keytest website (https://en.key-test.ru/), it turns out that the key still registers normally if pressed, only it does no longer seem to print any symbol at all. All other keys still work as expected. When connecting an external (Bluetooth) keyboard, the symbols can be printed with no problem. If it helps, I am using a German keyboard layout, for which the key in question corresponds to the CTRL key next to the arrow keys on the keyboard test site. If I switch to an English keyboard layout, the key also works as a CTRL key.

I suspect some software/settings issue is to blame for this. Have you ever encountered a similar issue, and any ideas on how to remedy this?