I followed these steps.
- Published extension (VS package) to the VS Gallery by uploading VSIX.
- Installed it to VS by selecting it from Extensions and Updates (experimental instance or normal instance).
- Incremented version number in source.extension.vsixmanifest. 1.3.23 changed to 1.3.24.
- Rebuilt VSIX and uploaded it again as a new version to existing tool page. Nothing else changed, just the version number.
- Reopen VS, go to Extensions and Updates > Updates > Visual Studio Gallery
It does not list my extension for update.
Oddly, if I go to Extensions and Updates > Online > Visual Studio Gallery (after uploading new version), it shows the new version. But it does not recognize it as an available update.