now I have a WEBMAIL BLOCK, but the summary box in the first page says "IDS BLOCKS - 0"...

Gabriele, when you navigate to the IDS blocks page, can you open the browser console window?  In the console please confirm that SignalR is working appropriately.  It sends the updates for the IDS counts.  If it is running correctly, you should see something like the image below.  Additionally, are there any API calls in the network tab that are failing or returning non-200 responses?

Actually I have IDS BLOCK box in the first page that counts "1", but in the detailed IDS BLOCKS page I see 2 WEBMAIL BLOCKS

This is what I actually see in console for IDS BLOCKS page:

Blank access token in interceptor.service
site-v-100.0.6898.30675.8d64f019ef63100.js:100 SignalR Init2, Connected: undefined
site-v-100.0.6898.30675.8d64f019ef63100.js:100 SignalR Start2
site-v-100.0.6898.30675.8d64f019ef63100.js:100 SignalR Started2
site-v-100.0.6898.30675.8d64f019ef63100.js:100 SignalR connection type: webSockets
site-v-100.0.6898.30675.8d64f019ef63100.js:5 SignalR Initted, Sending connect with auth details.
site-v-100.0.6898.30675.8d64f019ef63100.js:5 SignalR Connect success.
site-v-100.0.6898.30675.8d64f019ef63100.js:100 [SignalR Self Check] Starting... (qddz6d)
site-v-100.0.6898.30675.8d64f019ef63100.js:100 [SignalR Self Check] Sent request to server waiting response...
site-v-100.0.6898.30675.8d64f019ef63100.js:100 [SignalR Self Check] Got response from server: qddz6d
site-v-100.0.6898.30675.8d64f019ef63100.js:100 [SignalR Self Check] Got result from server. SignalR is working! Check PASSED.

news?

Gabriele, can you verify that you are running that latest version of SmarterMail 17, please?

It's the latest: 

SmarterMail Enterprise
Version: 6898 (nov 20, 2018)

Updated to the latest version today, the issue is not resolved.

With the latest version 6913 this issue SEEMS to be resolved.

I would like to keep an eye on the system for a few more days, then I will let you know if everything is OK