hydra-queue-runner is more anal about the format than Catalyst, so it was misinterpreting gc_roots_dir.
UQWA3UWFBTL4K2US2KWF5Z4ZQVOV2PKUZ3VINBSSHYAQTZ5ICKWAC 7I2VJDS6UO3W36E64RNRJTJ6ZEB5Y6EP3ZWUGZY4TQW25HJORBHAC LEHRDMCMXFOWQOUNHFJNNNKXKUNPS3UTUG2RR237FFAGD43L6QQAC 4J33F22TRXXW3WRI3KAF7DQZXQ7JH3A5XBNR7BJCKK7OFUF4AHSQC D3MDJONYWWNXVVZDKTPDQE2H2HGMF263LXKT57B2GYCOXNM3PPOQC PMDWFZHWNNA764E7A4TAMX7TN2SFPGWQXWPUETAYTFU6UJEOCYDAC KKHVM4KAM6I5B4KZPIKCEBWRB3LNYCFD7XIH4NCPGLNSMRCGJC6AC using_frontend_proxy 1base_uri ${cfg.hydraURL}notification_sender ${cfg.notificationSender}max_servers 25compress_num_threads 0
using_frontend_proxy = 1base_uri = ${cfg.hydraURL}notification_sender = ${cfg.notificationSender}max_servers = 25compress_num_threads = 0