The KCIDB schema specifies that a build's log_url must be a "URL of the plain-text build log file". I.e. it must point to a single plain-text file, which it should be possible to download and keep as part of the submission.
However, kernelci-backend sends URLs pointing to an HTML page (an automatic index of a directory) displaying links to multiple log files. E.g. https://storage.kernelci.org/stable/linux-4.19.y/v4.19.219/mips/ip27_defconfig/gcc-10/logs/ as seen in the attached sample submission.
Consider sending a link to the main (or merged) plain-text log file instead, and putting all the other log files into output_files.