Sometimes hangs

I have cache for about 5Gb. Sometimes it hangs on:
> restoring directory <...> from remote cache <...>
Target repository emty, disk and memmory free more 50%, CPU and network not used.
If OK, it works for 5 minus, if it hangs, it hangs for 1 hour and more, until build timeout.
How to debug it?

The report provides no file, test, or entry point. Start by reproducing a cache restore from the remote server and observe the “restoring directory” step under the reported disk, memory, CPU, and network conditions. Done means identifying why the restore can wait indefinitely and documenting or testing a bounded, successful restore.

Written by the indexing model from the issue text.