I’m running the latest versions of everything combined with SonarCloud:
SonarQube Scanner 4.2.0.1873
SonarCFamily plugin version: 6.7.0.15300
SonarQube server 8.0.0
Whenever I run a full build (e.g. on CI, but this is also replicable locally), the SonarCFamily cache is fully invalidated with 0 hits, even when just a single non-header file has changed. If I run an incremental build, then the cache works as expected.