Hi,
Since my original post I actually found out how to disable the shortcut but didn't post anything here because there was little interest in this issue (apart from one unhelpful reply
). However, you seem to be genuinely just as annoyed as I was, so hope this helps.
You need to go to Gaming > Global Settings > Performance Monitoring > Toggle Performance Logging Hotkey
You will see this is bound to Ctrl + Shift + L (so the shortcut is used - just buried).
To remove the shortcut (not an obvious process at all!) you need to click the Toggle Performance Logging Hotkey button, it will then ask to enter your hotkey, you then press delete - that is Del (not backspace, not esc or anything else - the Del key).

Congratulations, you now have now removed that annoying shortcut and can use ReLive if you so wish.
God knows what I've ended up logging because of this hotkey.