One of the most dangerous Visual Studio behaviors is building and running with a different configuration than you think.
You debug Debug, but the app actually runs Release — or worse, a cached build.
Why this happens
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Multiple startup profiles
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IIS Express vs Kestrel mismatch
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Configuration Manager not synced across projects
Life-saving fix
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Open Configuration Manager
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Ensure every project uses the same configuration
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Disable “Use global.json” if SDK mismatch exists
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Clear
.vs,bin, andobjonce after fixing
This prevents ghost bugs that only appear “on some machines”.