We've seen cases where the "Admin - Remove a member from a blob store group" task does not move all content from the target blob store into a new blob store. When this happens it fails silently, nothing is logged. At the end of the run it reports success, and removes the blob store from the group. After this, many build failures can occur since not all content was moved.
Expected: We need to find out what is causing these failures and get it fixed. If a blob cannot be moved the reason should always be logged, it should never fail silently.
Workaround: If you are affected by this bug add the blob store you removed back into the group at the bottom of its list of blob stores. Set the write policy of the group to "write to first" to prevent new content from being written to the old blob store.