See the original motivation in https://jira.mongodb.org/browse/DEVPROD-37675.

We discussed and decided that turning off any caching in patch builds for release variants was an acceptable solution to the problem in the above ticket. While this will result in slower compiles, these variants are rarely patch tested against. Any variant that is marked as release (e.g. it has a save_waterfall_* task) should never attempt to use the scons cache or remote execution of any kind.