We already got this LBUG twice :
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ASSERTION(mdd_object_exists(obj)) failed: FID is [0x20001a604:0xc9:0x0]
LustreError: 34372:0:(mdd_object.c:91:mdd_la_get()) LBUG
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It always occured after a MDS crash, shine fsck, shine start and during the Clients recovery timeframe.
Each time we achieved to restart the MDT/MDS using abort_recovery.

If we assume that the concerned+missing FID has been destroyed during the fsck on the MDT after a MDS crash for any other problem, and if we consider that there are no other possible scenario than such "external" action to lead to this situation (my opinion, but what do you think ??), can we think about to replace this Assert/LBUG with only a Warning message (at least during Client-recovery phase ...) ???