{{ arch }} evaluated to “arch1-windows-amd64-unknown” in one of my jobs using the default executor of the windows@2.4.0 orb during the restore_cache step. It typically evaluates to “arch1-windows-amd64-1_” instead, and indeed this is what it evaluated to during the save_cache step in the same job. This resulted in a cache miss even though the cached contents were the same without an accompanying cache store, so the consequences in our particular case were fortunately extremely minor. However, depending on how others are using caching, this unexpected instability of a template variable within a job could potentially result in more serious issues.
I have also hit this bug. Going to work around it by writing the architecture manually to the file system.