After days of attempting to find an solution, I've discovered what was preventing the LDIF importing for me. Ensure the following registry setting is set:
Key: HKCU\Software\Microsoft\Windows\CurrentVersion\WinTrust\Trust Providers\Software Publishing
Value: State
Type: REG_DWORD
Data: 0x00023c00
Our security policy mandates made us set this to 0x00010000 which was causing the failed import issues.