Usher and Chris Brown Tour: Singers Cancel Second Show Amid Feud

Usher and Chris Brown keep cancelling their shows ... the two singers have just pulled the plug on yet another one of their concert dates.

On Tuesday, the pair first cancelled their show at SoFi Stadium in Los Angeles on November 16. Now the artists are scrapping their gig at Hard Rock Stadium in Miami, Florida, on December 6, according to Ticketmaster's website.

The good news is that ticket holders will be fully refunded for both shows.

No reason was given for the cancellations ... but, as you know, TMZ broke the story about tension between Chris and Usher.  

Last week, TMZ broke the story that Chris and Usher got into a heated argument backstage at their show in Atlanta, Georgia.

We're told the dispute erupted after Usher and Chris didn't see eye-to-eye on when to kick off the performance as fans struggled to arrive on time due to traffic. 

Our sources say Usher wanted to promptly hit the stage, while Chris wanted to delay the show to accommodate the fans. We're told their issues remain unresolved and their relationship is "still icy."