Wikipedia (en):
During May's guitar solo, the lead on his guitar became disconnected and the guitar solo stopped for 20 seconds (as seen on the DVD but the 20 seconds was reduced to 3 seconds on the album version of the performance). A roadie had to help him get his guitar working again.
Also, drummer Roger Taylor did an impromptu 30-second drum solo before "Under Pressure" whilst May got his guitar fixed. Taylor had stopped doing drum solos (he last performed one in November 1981) so this was the only time he did a drum solo post-1981 with the original lineup of Queen. The next did not occur until the Queen + Paul Rodgers Return of the Champions Tour in 2005.
Roger usually plays his solo before starting Under Pressure.
Was he kept on playing drums in order to buy time?
Indeed, Roger had the brief solo spot before Under Pressure at the last few shows of the European/UK legs in 82 (starting in Hamburg). Maybe he missed playing it in Keep Yourself Alive.. ?