Windows 11 might have just had its Chernobyl moment. AMD and Microsoft already confirmed that the new operating system increases L3 cache latency by 3x on Ryzen CPUs, but it can actually be as much as 6x slower, according to independent testing. Cache latency can affect performance in many applications, including games.

Want even more big numbers to show how broken things are with Windows 11 on Ryzen? The benchmarks also show that Windows 10’s L3 cache bandwidth can be up to 12x faster than when running on Windows 11, according to testing by Paul Alcorn of Tom’s Hardware. Oof.

The bad news comes just after AMD and Microsoft jointly announced the 3x cache latency increase, which they said could reduce gaming performance in lighter-duty esports-style games by 15 percent on Windows 11. Less latency-sensitive applications and games could see to 3 to 5 percent slowdown on Windows 11, the companies said.

In the Tom’s Hardware testing, AMD CPUs with more than eight cores suffered the most. Alcorn found a Ryzen 9 5900X’s L3 performance in the AIDA utility on Windows 10 was about 10.54 nanoseconds. The same system running Windows 11, however, exhibited 29.23ns. Further testing by Alcorn found a Ryzen 7 3800X suffered a massive 6x increase in latency compared to Windows 10. Intel’s much-maligned 11th gen Core i7-11700K, however, had minimal impact from the new OS.

The good news is Microsoft and AMD have said they have identified the problem and a fix is expected this month. Sadly, that good news follows some bad news, as a patch for Windows 11 released yesterday apparently increased latency on Ryzen even more, as confirmed by TechPowerUp and TechSpot.

The L3 cache performance on Ryzen is addition to another bug in Windows 11, which doesn’t recognize AMD’s “best core” feature either. This bobbled launch on AMD’s popular Ryzen platform isn’t a great look for Microsoft’s new OS, which is still fighting headwinds from owners of older PC hardware that isn’t supported. As a reminder, we recommend most PC users skip Windows 11 for now until more of the kinks are worked out.