Failed Upload media wordpress

Greetings
in last weekend we updated 4 server machines all equipped with ubuntu 16.04 and Plesk 17.8.11. Last day we are unable to upload media in website hosted in webspace on one machine. Wpress backend shows a generic http error, and, most important, nginx after a failed upload attempt goes in 504 timeout for several seconds( depends how many media are upload at same time, more uploads, more time to restore from 504).
In wpress logs are not visible errors.
At the end we found the issue is related to yours plugin w3 total cache.
After disabling it media uploads restarted working.
Thanks,