Trojan:MSIL/Lazy.NNL!MTB flags every fresh build of a legitimate .NET assembly (MSBuild ResolveAssemblyReference blocked)

I'm getting a consistent detection — Trojan:MSIL/Lazy.NNL!MTB — on a first-party .NET class library DLL that I compile locally from my own C# source (not downloaded, not third-party). Every clean rebuild produces byte-identical output and gets flagged the same way, while 40+ other projects in the same solution, built the same way, are never touched. It's now blocking MSBuild (MSB3248: file contains a virus) and stopping my local builds entirely. Has anyone seen this specific signature false-positive recently, and what's the fastest path to get it corrected? Already tried Update-MpSignature — no change.