During OSD we found that the step to enable bitlocker was not storing the recovery key in the AD, this is because sccm won’t process any group policies until the task sequence is complete. To get around this problem you can export HKLM\SOFTWARE\Policies\Microsoft\FVE and create a package then add a run command line step using that package to the task sequence before the enable bitlocker step:
REG IMPORT BitLockerPolicy.reg.
Be sure to disable 64-bit file system redirection.
Thanks Martin Wüthrich -