[Gameplay] Cannot Open Shop & Experienced a Green Screen

Cannot open shop. When clicking on shop, it does not open. Instead, it acts like I pushed the C button to see more character stats (something that should also happen when the shop opens). Pressing P to open the shop exhibits the same behavior. Clicking on my gold inventory to open the shop exhibits the same behavior. Consequence is that I am unable to open the shop or buy any items at any point in the game. All other in-game behavior is normal, i.e. I can level up spells and cast them, I can recall and move and attack enemies and such.

What I did to attempt to fix it: Reboot game. Repair game using the repair option in the menu.

What actually fixed it: Changing my monitor resolution to the recommended resolution for my monitor (I changed it to 3840x2160 from 1920x1080).

How often this has happened: Occurred once, although persisted over 3 games until I corrected the resolution. Initially on Summoner's Rift, second game was on Twisted Treeline.

Running Windows 10 with a triple-monitor setup. Main display is a Samsung 28" 4K monitor. To either side of that I have two Samsung 226BW monitors. All three monitors are being driven by a single Radeon R9 290 graphics card, using DisplayPort for the 4K monitor and DVI for the other two. Normal FPS with League on highest graphic settings is over 100.

To start off, I was playing a game against AI with a friend who is new to the game (resolution was set at 3840x2160). Mid-game (I already had sighstone and maybe boots and Frostfang upgrade) my main monitor turned green. Solid green, no cursor or anything visible. I struggled to Alt+Tab out of the green screen and was eventually able to use Task Manager to force League to close. I then changed my Windows display settings to make one of the other monitors the "main display" in Windows 10 so that I could rejoin the game and finish it. This automatically changed the resolution in-game to 1920x1080, and I started experiencing the Shop issue.

After the game ended, the green screen persisted. So, I rebooted my computer and normalized my Windows display settings. This corrected the green screen. However when starting a new game with League running on the 4K monitor, the Unable to Shop issue persisted. I couldn't figure out how to fix it during this game, so I finished the game and tried repairing the client. In my third game, a Custom game, I tried changing the resolution back to 3840x2160 and this made the problem go away.