There are two entries for the two different things (1) Rental real estate enterprise if claiming safe harbor and (2) Aggregate business number. They are different things. 

(1) 

Rental Real Estate Enterprise Number, if Claiming Safe Harbor

Enter the rental real estate enterprise number to claim the safe harbor treatment under Rev. Proc. 2019-38. To be eligible, separate books and records must be maintained for each property, 250 or more hours of rental services must be performed, and the property may not be rented under a triple net lease agreement.

(2) 

Aggregate Business Number

Enter a number to aggregate two or more businesses. All businesses with the same number will be aggregated together.

NOTE: SSTBs may not be aggregated. See Publication 535 for more information.

Check your input - put the same number, like maybe 1 in the box for all the rentals you want to do whatever to. Maybe to keep them separate use 2 for those that you want to aggregate.