Check is there any User exit activated , because 5 no's difference is coming.
Take ABAPer help to check the changes or what is the cause to that , he will debug the customer number range program then he can come to know what is the cause.
I hope it will help you,
Your customer numbers are proposed by the system by the difference of 5, this means therev is a buffering of 5 nos.
Gop to J1i9 / SNUM transaction, put number range object as " Debitor " , go inside it & remove ( blank ) the buffering field of the number range. The customer numbers will be continued from next time.
Rewards points after the problem is solved.