Report Server can't create New Scheduled Refresh Plan

Hi,

After a deep check of all messages related to the issue, I would like to open a new one.

The issue, as it is said in the subject, is that we are unable to create a New Scheduled Refresh Plan.
On portal side we are getting: "An error has occurred. Something went wrong. Please try again later."

In the log file the message that may somehow help us: "|ERROR|16|'OData' exception occurred: 'System.Net.WebException': The request failed with an empty response.."

We are using Power BI reporting server - SQL Server Enterprise with Software Assurance. Product Version 15.0.2.540

Will highly appreciate to get any help / advice.