Can't save dataflow when linking a table from another dataflow; Unknown exception error

When I'm in Dataflow A and I link to a table in Dataflow B and go to save the changes it gets this error after doing all the Validating Queries (of which it passes validation):

Then it shows this "Couldn't save changes" error on Dataflow A:

Hitting Retry results in the same error. There is no detailed information on what could be going on. The only way to save Dataflow A is to go back and Edit tables in Power Query and delete the linked table.

However, if I link a table in Dataflow C, it works correctly with no issues. 

Please note I've been able to link to Dataflow B in the past.

What could be going on here with Dataflow B? How can I figure out how to resolve this when the only error message I get is an unhelpful "Unknown exception"?