Blue Origin encountered an issue during recent BE-4 testing according to Michael Sheetz:

During a firing on June 30 at a West Texas facility of Jeff Bezos’ space company, a BE-4 engine detonated about 10 seconds into the test, according to several people familiar with the matter. Those people described having seen video of a dramatic explosion that destroyed the engine and heavily damaged the test stand infrastructure.

ULA is pushing back on the notion that this will have an impact on Vulcan:

“The BE-4 testing issue is not expected to impact our plans for the Vulcan Cert-1 mission.” The company noted that the engines for Cert-1 “successfully passed acceptance testing” and are qualified to launch.

It’s difficult to know just how serious this is without more information about the failure and the intent of the testing but hopefully Blue Origin and ULA will get both the BE-4 and the Vulcan sorted soon.

Update: Tory Bruno tweeted some good news.