Refresh Problems with Sharepoint

We are suddenly having intermittent problems with refreshing datasets that connect to Sharepoint, and nothing has changed in our systems, so I'm wondering if anyone else has seen this recently. It started about the beginning of June. For the most part, the datasets are accessing Excel files hosted in various folders in our Sharepoint site. Often the refresh works when retried manually or on the next scheduled refresh, and always works fine in Desktop. 

Here's what I'm seeing as errors:

We couldn't parse OData response result. Error: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.

"We're sorry, an error occurred during evaluation.

"Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.