Is there a known issue/limitation with Dashboard Table Components in Lightning?  Specifically it does not appear that you can add more than 2 columns to a "new" Dashboard Table Component in Lightning.  The only way I have been able to to it is create the Report, Chart, and Dashboard in Classic UX and then switch to Lightning UX and clone the Dashboard.  However the Table DB Components still can't be edited in Lightning UX, only other Component Types (Bar, Doughnut, Line, Scatter, etc) can be edited.     

I can't find anything listed here:

DOCUMENTATION

Reports and Dashboards: What’s Different or Not Available in Lightning Experience | Salesforce 

https://help.salesforce.com/articleView?id=lex_gaps_limitations_analytics.htm&type=0&language=en_US&release=208.9