Hi,
Woudl you check what is the buffering setting for Busines partner number range object (I think BU_PARTNER) in SNRO?
If number range bufferieng is switeched on an interval of numbers is stored in the shared memory of the application server Standard setting in SAP for other objects such as LIV invoices is 10 and then the system assigns an interval of 10 numbers to a user. After this user posts 10 invoices and therefore all numbers of this interval are used up, the system assign the next interval of 10.
Hope that this helps
Cheers
taro