SharePoint/Office365 API is really slow and only works sometimes

The Office 365 API is extremely slow and works occasionally.  Have been using it for a couple of years now...performace is only getting worse.   We are tired of having to wait a half an hour just to load a query preview or apply any changes. 

Some days work better than others.  Overall, your API should work consistanly, we a paying for Power BI premium and can't make any reports due to the fact it takes too long just to query the data. 

Connection Error Message - Extremely Slow SpeedsConnection Error Message