So I have had a Drobo 5N at a client site for 6 years, perhaps a little more. Yesterday the client could not access data on it. When I got there the unit had a funky light sequence, from Drive 0 (top) down was yellow, red, nothing, yellow yellow. I rebooted the device and it went into data protection rebuild mode and we could see the data. Checking the status of each drive had drives 1 and 2 with warnings but could not find the error. I ordered 5 new drives and one at a time, each time allowing data protection to finish, replaced all 5. Now 4 of the 5 drives show as SSD though they are HDD and drives 1 and 2 have warnings again, drive 1 has a warning and is the only one of the new drives that does not show as an SSD. I am puzzled.
Could be you inserted SMR drives which are not compatible. What are the drive models you installed?