Parallel downloads were introduced in 45c00abe40503c8ecc991abe17490395dcb54fc1 to speed up RTD build (!25). Unfortunately, when more than 1 core is used and at least one of the file is duplicated in the list of missing kernels (within the number of core window), the 2 thread will compete and the second one will generate an `FileExistsError`. This situation appended for JUICE with the mk `juice_crema_5_0.tm` where `juice_mga_crema_5_0_default_f20160326_v01.bc` is duplicated [l.96 and l.99](https://repos.cosmos.esa.int/socci/projects/SPICE_KERNELS/repos/juice/browse/kernels/mk/juice_crema_5_0.tm?at=refs%2Ftags%2Fv310_20220517_001#96,99) in SKD v310 and v320. This issue was reported to the ESA Spice service on July 27th 2022 and should be addressed in the release. --- __Possible fix:__ Ensure that the download list [`missing`](https://juigitlab.esac.esa.int/datalab/moon-coverage/-/blob/45c00abe40503c8ecc991abe17490395dcb54fc1/moon_coverage/spice/metakernel.py#L269) in the `MetaKernel.check()` function contains a unique list of output files.