If rebuildbcd fails, you must manually recreate the store:
: Use the bcdboot tool to copy fresh boot files from the Windows directory to the EFI partition: bcdboot C:\Windows /s S: /f ALL 6. Solving Post-Update Boot Loops windows server 2012 r2 boot repair
sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows windows server 2012 r2 boot repair