Rigs 6*470 4Gb
Have problem with one card for rigs.
Performance: 7.20 sol/s 8.40 sol/s 7.93 sol/s 7.07 sol/s 0.93 sol/s 6.67 sol/s | Total: 38.20 sol/s
Performance: 7.33 sol/s 8.27 sol/s 7.80 sol/s 7.13 sol/s 1.00 sol/s 6.33 sol/s | Total: 37.87 sol/s
Performance: 7.13 sol/s 8.07 sol/s 6.20 sol/s 8.80 sol/s 0.87 sol/s 6.80 sol/s | Total: 37.87 sol/s
Performance: 8.20 sol/s 8.40 sol/s 7.53 sol/s 7.53 sol/s 0.73 sol/s 8.13 sol/s | Total: 40.53 sol/s

What is the reason?