Flow problem following the migration to sophos xg 18

From which version did you come and whats your current throughput? How did you measure your throughput? 

Did you enable anything in the new engine? 

My current speed is between 20 Mb / s while if I connect to my provider's router it is 400 Mb / s

I really didn't do anything after the update

Check you wan settings in the XG.

ian

This is the first thing I did.
My switch is also good in 1 Mega.

Your modem should be in bridge mode so you get full benefit and control.

ian

I kept the same configuration as with version 17.
I simply updated the system from 17 to 18
On my provider's modem, I created a DMZ and I connected my sophos router to the DMZ

You end up with double Nat, which could be confusing some of the migrated/new features in v18. Have you been through and deleted all the sd-wan policies?
ian

Sorry but I can't understand why NAT could reduce my internet speed so much
That he could prevent me from going out on the net I would understand.

Finally I came back to 17.5.
And now even in 17.5 I have a sub of slowness.
That I did not have before the passage in 18