We found out this issue caused by incompatibility with Form Mail plugin from Adaptavist . Scaffolding plugin will be disabled after a restart, if the Confluence instance has Form Mail v4.1 installed (this issue does not happen with previous version of Form Mail plugin).

For temporary workaround, kindly please:
1) Disable Form Mail plugin
2) Follow this KB to clear plugin cache
3) Enable Form Mail plugin

Our developers will work on the bugfix soon.