Cache is used for only one of jobs that are running in parallel
It looks like if two jobs are running in parallel, the second job doesn't uses existing cache(so everything is being downloaded from internet again)
This is a feedback from a user, but I think I saw the same once.
Source(in Russian): https://habrahabr.ru/company/softmart/blog/305436/#comment_9697292
Edited by Jason Yavorska