Regarding Guard Duty

Does your KMS key policy grant guardduty as stated in Guardduty Setup Documentation. KMS key policy would be as below:

   {    
       "Sid": "AllowGuardDutyKey",
       "Effect": "Allow",
       "Principal": {
           "Service": "guardduty.amazonaws.com"
       },
       "Action": "kms:GenerateDataKey",
       "Resource": "arn:aws:kms:Region1:444455556666:key/KMSKeyId",
       "Condition": {
           "StringEquals": {
               "aws:SourceAccount": "111122223333",
               "aws:SourceArn":    "arn:aws:guardduty:Region2:111122223333:detector/SourceDetectorID"	
           }
       }
   }

For bucket policy, follow the section Granting GuardDuty permissions to a bucket in the above mentioned documentaion.

Bucket and KMS key policy are two most common places, which prevents guarduty to write logs.

Hope you find this useful.

Comment here for additional questions.

Abhishek