Fortigate 90D High CPU Usage

Currently I'm running the Fortigate Firewall 90D as internet gateway, it's covering about 50 users to internet. I have a concern regarding the CPU usage. There is 99% utilization. I used the command "diag sys top" and I got the result as below.  The process "miglogd" using almost 90%. I have tried to disable the disk log setting. But it still high. Do you have any ideas?

Run Time: 0 days, 15 hours and 16 minutes 5U, 0N, 94S, 1I; 1838T, 1098F, 173KF miglogd 78 R 89.1 1.9 httpsd 159 S 2.9 1.3 ipsengine 143 S < 2.1 5.1 proxyworker 98 S 1.5 1.7 httpsd 65 R 1.5 1.3 scanunitd 458 S < 0.5 2.1 newcli 437 R 0.5 0.8 miglogd 142 S 0.3 0.8 ipshelper 119 S < 0.1 1.1 httpsd 461 S 0.1 0.9 src-vis 110 S 0.1 0.7 forticldd 88 S 0.1 0.6 httpclid 92 S 0.1 0.5 initXXXXXXXXXXX 1 S 0.1 0.5 scanunitd 459 S < 0.0 2.1 scanunitd 100 S < 0.0 2.0 pyfcgid 456 S 0.0 1.3 pyfcgid 455 S 0.0 1.3 pyfcgid 457 S 0.0 1.3 pyfcgid 453 S 0.0 1.3

Thanks,

Putmano