Apparent multiple execution of generate.tasks jobs

Consider this task https://evergreen.mongodb.com/task/mongodb_mongo_master_enterprise_rhel_62_64_bit_display_sharding_ese_patch_b3b494a72f0e19d7556bee627da7ae9b79e26a03_5dadc8ef30661551b09da831_19_10_21_15_04_43. (There are many similar examples in that version.) The generator clearly finished, since it generated tasks. However, there is an error that returns early, which suggests there must have been multiple executions.