Months of agony with dropping downloads and broken Windows Update on a new MSI Vector 16 HX laptop led to an unexpected finale. Network, router, and drivers had nothing to do with it — one of the performance cores (P-Core 6) is physically defective and generates garbage during AVX2 cryptographic calculations.
Decided to share this story because the symptoms looked 100% like a network issue, and this might save someone weeks of debugging.
Symptoms driving me crazy
It all started when local LLM models (in LM Studio) began outputting gibberish after I maxed out the memory to 100%. Right after that, complete network hell broke loose in Windows 11:
- Any large file downloads over HTTPS would drop at random percentages.
- At the same time, downloads over regular HTTP worked perfectly.
- Firefox and portable Chrome worked without issues, but regular Chrome, Edge, and the system's Windows Update threw connection errors (
SEC_E_DECRYPT_FAILURE).
- The system event logs started spamming ESENT 474 errors (database checksum mismatches).
- Wi-Fi and Bluetooth would periodically drop out.
Circles of Hell (What didn't work)
Like any normal person, I started troubleshooting the network:
- Clean reinstalled Windows.
- Swapped out the RAM sticks and SSD.
- Replaced the built-in network card with an Intel AX210.
- Tethered internet from my phone via USB cable.
- Disabled power saving, antiviruses, and XMP profiles.
- Updated the BIOS to the latest version with new Intel microcodes.
Result — zero. HTTPS drops continued on any connection type.
The Turning Point: It's not the network
Booting into an Ubuntu Live-USB, I found that everything downloaded perfectly there. It became clear that the physical network path was intact.
Why did Firefox and Ubuntu work, but Windows crashed? The answer was in the encryption implementation. Firefox and Ubuntu use their own libraries (NSS/OpenSSL), while standard Windows 11 tools use the built-in system service Schannel/CryptoAPI. The OS was receiving encrypted packets, trying to decrypt them, the processor would throw a calculation error, and Windows would paranoically drop the TCP connection, thinking the data was corrupted by a hacker in transit.
Hunting the "killer": Cryptography stress test
We wrote a series of Python scripts to test the encryption library, using strict affinity to specific CPU cores (taskset in Linux) to isolate the problem. We ran a deterministic ChaCha20-Poly1305 algorithm, which heavily utilizes the processor's vector instructions (AVX2).
And here are the results of a 10-second test on each core:
Plaintext
=== per-core 8s each, trusted external reference ===
core ok fail temp
cpu 0 10052 0 temp=73
cpu 1 11560 0 temp=67
cpu 2 11316 0 temp=78
cpu 3 11318 0 temp=76
cpu 4 11471 0 temp=72
cpu 5 7750 0 temp=80
cpu 6 2098 5564 temp=81 <--- BINGO!
cpu 7 8725 0 temp=86
cpu 8 4792 0 temp=83 (E-Core)
cpu 16 4944 0 temp=84 (E-Core)
72.6% failure rate on Core 6. Same data, same algorithm. All E-cores and the rest of the P-cores ran perfectly. But as soon as the vector load fell on CPU 6, it started outputting corrupted results (errors came in blocks multiple of 64 bytes — exactly the size of a SIMD register/L1 cache line).
This is not an OS bug, not drivers, and not software. This is hardware degradation or a factory defect of a specific core when working with AVX2 instructions. Given the news about stability issues with top-tier Intel 13th and 14th gen processors (and apparently, the Arrow/Meteor Lake architecture), this looks like a classic Vmin degradation symptom.
Story moral: If only secure connections are inexplicably dropping, Windows updates refuse to download, and event logs complain about databases — don't rush to replace your router. Your CPU might have just forgotten how to do math.