This only affects 4.2.4 binaries running with FCV 4.0. With FCV 4.0, we don't use WiredTiger checkpoints for backups. But when we start-up with queryable backup mode, WiredTiger will use the callbacks for the writeable API implemented in 4.2.4 when it shouldn't.

On 4.2.4 binaries with FCV 4.0, the recommended workaround is to add these options to the config:

• storage.wiredTiger.engineConfig.configString: ",readonly=true,"
• storage.journal.enabled: false