I've anecdotally heard that setting the game to run as an admin and putting it in windows 7 compatibility mode (regardless of the OS you're running assuming you're on a PC) will fix this. I'd recommend just running it as an Admin first then changing the compatibility settings if that doesn't work.
Steps to do that:
1.) Right click the LoL shortcut > properties > compatibility tab
2.) Check the "Run this program as an admin" box
3.) Try again
4.) If it's still messing up try clicking the "Run this program in compatibility mode for:" box and select windows 7
If that doesn't work below are a few steps RIOT will have you take to deal with any issue:
1.switch to a public DNS here is the How-to link (https://support.leagueoflegends.com/entries/26932010-Troubleshooting-Connection-Issues#wq4)
2.Disable your IPv6. https://support.leagueoflegends.com/entries/26932010-Troubleshooting-Connection-Issues#wq3
Sync your windows clock - https://support.leagueoflegends.com/entries/35999450-Issues-with-the-League-of-Legends-Store-and-PvP-Net#wq8
4.Shut the Windows Firewall Service to make sure it isn't interfering with your connection to our servers:
Press Windows+R
Type services.msc and hit enter
Scroll down and find Windows Firewall in the list
Right-Click on "Windows Firewall" and select "Properties"
Change "Startup type" to "Disabled"
Hit "Ok"
Do the same for the "Windows Defender" Service
Reboot your machine
if all of this fails perform a clean boot. - https://support.leagueoflegends.com/entries/28849700-Bug-Splat-and-Game-Crashes#wq6
Hope something here helps.