Refresh fail - Invalid JSON? (data loads in power query, but fails to refresh)

[unicorns]

My refresh is failing but my data loads just fine in the Power Query preview section. All I'm doing is appending a query to a table then removing duplicates. any idea why this report refresh is failing? I'm not doing anythign special other than putting two tables together, then removing any duplicates. Any help would be appreciated!

[d_gosbell]

The preview window only loads a subset of the data. This possibly means that you have some invalid data later in the data source.