CRM Online OData feed from Power BI

I'm connecting to very large, bespoke CRM system that has nearly 300 fields in the IncidentSet table (Case).  there is over 100 required fields and I'm having issues trying to download the data with getting a host of errors.

I keep receiving a 404 DatSource.NotFound error (having already successfully accessed and downloaded the data) and then when I do get  access to the data it only loads 51 rows, when earlier in the day the query returned 51,000 rows. 

Can anyone let me know of restrictions of the OData Feed for CRM as I think I bouncing off some limits somewhere....

Thanks