Hi @Mirko Salicini ,
I'm glad to hear you solve the problem ,if you have any issue about SharePoint, you are welcome to raise a ticket in this forum.
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others.". and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
[SharePoint Online IRM Service returns: 409 CONFLICT]
I'm here for a strange problem that occours on my O365 tenants.
Yesterday the IRM service of SharePoint Online stopped working and returned a blank page when a user try to open a docuemnt with Edge.
With "Edge developer tools" we found a strange return message: 409 CONFLICT
Our customer has enabled this service one year ago.
Nobody has chaged any configuration at the time.
We also try to refresh IRM configuration and enable / disable IRM from the docuemnt library, but nothing has changed.
So we have reproduced in a test evirorments, in another tenant the same configuration, but the problem persist.
Our next step it's open a ticket in Microsoft.
Magically from 11 July everything working good.
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