Load of the server increased from 20.34 to 5638.41 or similar value, but during this time none of the VM has taken more load than usual.
The root cause of the high-load was non-available Cloud storage due to failed chunk-servers.
To avoid high load in future needs to reconfigure pstorage using the following settings:
Number of chunk servers - 5 or more - this will speed-up the storage and give more redundancy.
Recommended replication parameters are 3 norm: 2 limit.