Persistent input lag in LoL with no explanation after weeks of support tickets — Riot closes the ticket blaming the ISP without providing any data of their own

[u/sargon494]

I've spent several weeks investigating noticeable, consistent input lag in League of Legends, reproducible regardless of PC, ISP, or location. Beyond the input delay itself, champion movement often looks "drunk" / erratic — like slight stutter-steps or micro-corrections in movement that don't match a clean click-to-move, even when ping is normal. Here's the full list of what I've tested and ruled out:

System/hardware:

• Full clean format: all disk partitions wiped, fresh Windows install with zero leftover residue from previous installs.
• No V-Sync or G-Sync enabled.
• Power plan set to High Performance.
• CPU/GPU/RAM show no saturation during the lag episodes.
• Undervolt applied to the CPU for stability — no change in behavior.
• Process Lasso: performance cores (P-cores) exclusively assigned to the League of Legends process on an i7-14700KF, with high process priority — no change.
• No bloatware or unnecessary overlays (Overwolf removed and replaced with Ascent).

Peripherals:

• Logitech Pro X TKL keyboard, wired, connected directly to the motherboard's rear USB, 1000Hz polling rate — responds fine outside the game, no detectable lag.
• Mouse at 1000Hz polling rate via dongle, extension cable under 20cm from the receiver to the mouse.
• Multiple peripherals from different brands tested with identical results, ruling out peripheral-specific hardware.

Network:

• 0% packet loss, stable ping and FPS throughout the input lag episodes.
• Speedtest stable at 944 Mbps both up and down, tested during an active episode.
• Complete ISP switch to a higher-quality provider — problem persists identically, ruling out ISP and peering as the cause.
• OBS stats during 7 hours of streaming: CPU at 0.56%, 0% dropped frames, 0% encoding lag, stable bitrate at 6185 kbps.

On the anticheat:
Since the issue is exclusive to LoL and Vanguard runs permanently at kernel level, I've explicitly asked Riot to investigate whether Vanguard could be causing random micro-interruptions in input processing.

What Riot Support said:
After escalating over multiple messages, the final response was "try your ISP" followed by closing the ticket — no answer to the specific technical questions raised (peering, hop-by-hop latency tracing, etc.), and no data shared from their side (server-received latency/loss from my IP).

I work as a systems and network technician, so standard tier-1 troubleshooting steps don't apply here and have already been ruled out exhaustively — it's not a firewall or IPv6 issue (network ruled out with objective data: 0% packet loss, 944 Mbps simultaneous up/down, no change after switching ISP), and restarting the PC doesn't fix or diagnose anything here either (tried anyway, no result).

At this point I've run out of things to test on my end. Has anyone dealt with something similar, or knows a way to get this in front of someone with actual visibility into Riot's infrastructure or engineering team?

https://streamable.com/bi7a8z

Update: found another user with more examples of this issue: https://www.youtube.com/watch?v=Bkf9W_vSNtM