I'm not sure if you are using Denodo Enterprise or Denodo Express, but plese note that Denodo Express will limit the amount of concurrent queries to 3.
There are a number of possible causes for this, such as query concurrency at the data source or the Power BI Gateway hitting its configured concurrency limit, which by default is set to an "intelligent" value, but can be affected by the issue of multiple concurrent queries, especially if the Gateway is being used at the same time for other data sources (other than Denodo).
I suggest checking the query concurrency levels using the Denodo Query Monitor, and the queries that are reaching Denodo from its ODBC interface (both the queries themselves and their execution times) using Denodo Monitor or the Denodo Diagnostic and Monitoring Tool.
If after checking all that you still have issues, if you have a valid support user, please open a support ticket in the [Denodo Support Site](https://support.denodo.com/), so the Support Team can review the issue in detail.
Hope this helps!