When a drive enclosure (JBOD) is powered off abruptly as in the case of a power outage, the drives may not come up before the sensor head is powered up. The drives are seen as missing and then once they are powered on and ready are seen as foreign to the sensor. This may also happen when a single drive is replaced.
The resolution is simple once you determine the adapter number from lsi-show. The adapter number is either a0, a1, a2, or a3. It is found by running lsi-show and looking under the Id in the "Controller Information" section. You will need to run lsi-show to find the failed JBOD and then megacli -cfgforeign -import -a1. Change the 1 to the Adapter number in your case.
For example, this is for Controller for Adapter a1:
Id Serial No Firmware Encl LD PD Product Name
a1 38T012N 3.130.05-2086 2 2 24 PERC H810 Adapter
Look for the Physical Drive Information that contains the "Unconfigured(good), Spun Up" drive. For example,
Physical Drive Information
Id E:S Status FC Size Inquiry
9 12:0 Unconfigured(good), Spun Up Foreign 1.819 TB SEAGATE ST2000NM0023 GS0AZ1X0NUAD
8 12:1 Unconfigured(good), Spun Up Foreign 1.819 TB SEAGATE ST2000NM0023 GS0AZ1X0LNYK