I have a same problem with the current version of Ubuntu 18.04.1 LTS (Bionic Beaver) with kernel 4.15.0-42-generic.
I have a new RAID 5 array with 4 12TB drives. As the array is being initialized, it takes 3 to 10 minutes to reach a kernel bug (under the additional system load less than 1 minute).
I have a same problem with the current version of Ubuntu 18.04.1 LTS (Bionic Beaver) with kernel 4.15.0-42-generic.
I have a new RAID 5 array with 4 12TB drives. As the array is being initialized, it takes 3 to 10 minutes to reach a kernel bug (under the additional system load less than 1 minute).