Trio exchange disconnection on calendar event cancellation

Hello, I have a Trio 8800 fw 5.9.0.11398, generic profile, integrated with OTD. I am using OTD integration with service account and passtrough authentication. My exchange server on the Trio is https://otd.plcm.vc/EWS/Exchange.asmx and on the Trio I configured the username and password of the O365 room mailbox that I want to connect. Everything works fine, on the OTD panel I see the Trio connected to OTD and OTD connected to O365, calendar events are visible on the Trio and I am able to join meetings.

All works fine until an event is cancelled. As an example, if from my personal mailbox I create an event and invite the room, it is correctly displayed on the Trio.... then from my Outlook I delete the event (and send the cancellation) and a few seconds later the Trio raises the error 

"Failed to connect to exchange server: re-enter credentials to access exchange services"

Logs on the Trio say:

0718120448|pgui |4|00|onNetworkError: error occurred 204 
0718120448|pgui |4|00|New credentials needed for accessing Exchange Web Services, deactivating to wait for new credentials
0718120448|pgui |4|00|Stopped access token service
0718120448|app1 |4|00|EC has failed to authenticate with server
0718120448|pgui |4|00|Exiting EC for sign out.

The OTD panel shows Trio connected to OTD but OTD not connected to O365 with the error "calendar access not permitted". If I go on the trio, settings, basic, login credentials and I press submit without changing anything, it works again.

I tried this https://knowledgebase-iframe.polycom.com/kb/viewContent.do;jsessionid=D80E88F3E9B2AFC3AD3E732B659ECDD9?externalId=33896&sliceId=1

with the following settings

exchange.ADerror.retryCount="2"
exchange.ADerror.retryPeriod="10"
exchange.error.retryCount="2"
exchange.error.retryPeriod="10"

but did not solve the issue. Honestly I do not know if these setting are correct.

Thank you for your help.