I get this error a lot.
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So I did some research and found out people get it by having a LoL client already loading/opening and trying to open it. So I think when the bot goes to restart the client, it doesn't wait long enough for the last client it closed to full close or something to start the new client. I never get the error when first starting so I am pretty sure it has to do with when it restarts and not waiting long enough
I am going to try to make my delay a little longer, but if it doesn't work, then the developer will need to check if the process if already running and close it.
Edit: I just noticed while my game was loading up the match to afk, it opened up another patcher (where you press play). I noticed it wasn't on my taskbar, but I found it in my processes. So maybe that is the hidden process that causes the error.