Hi
Usually, this does not happen... Dep Start Date is auto populated based on Cap date and Period Control Key of Depreciation Key
Was it manually removed? Can you check the change logs of this asset? (AS02 > Enter Asset No > Press Enter > Environment > Change docs > On Field)
Also, is this the only case having this issue? If yes, then i suspect some manually removed it
Otherwise, if all assets have this issue, then you can check the period controls in OAYH.. You can generate them from OA84
Br. Ajay M