Here’s everything you need to know.
The error message says “trouble fetching information for this player (Error: 5C). Affected players should quit and log back in if this persists.” But after players reset the game, the error message often still persists.
There’s a number of ways to fix this bug, and while it’s largely unknown why the error occurs in the first place, it can easily be solved.
How to fix the error
The bug seems to be somehow related to internet connection. It’s unclear why, but resetting your router is one possible solution. Instead of closing the game before resetting the router, reset it immediately, then test if the error message persists. If it does, you can re-log in and the problem should be fixed.
If this doesn’t work, there are a few other options that could help solve the issue.
If you have access to more than one League account, log into your alternative account, then log back into your main account. This, for whatever reason, often works.
If the error message still continues, you should try disconnecting from your router, opening and connecting to a hotspot with your mobile phone, and then logging in and pressing play. You should then close the hotspot and reconnect to the router.
If all else fails, simply use League’s repair tool and the error message should automatically be fixed. The repair tool can be found here and it works with both Windows and OS users. The repairing process may take some time, though, so it should be a last resort.