If you look in LD 90 there may be an entry that corresponds to this number(s), That entry will be associated with an RLI. When you have that, go to LD 86 and prt RLB and enter the RLI # at the prompt. When that prints out you will see each entry (possibly more than 1) has a DMI. In LD 86 again, PRT DGT, enter the DMI and it will show you what the system is doing to the digits, in this case deleting.
The easy solution is to go to LD 90 and find another similar number that works externally, then use that RLI with the number you are having issues with. You can change that in LD 90, then test.