Hey Jonathan,
From what it looks like (correct me if I'm wrong)
You have both a Customer and Customer Lead '@PT ASTRA OTOPARTS TBK'
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if I go into the Customer 'Yoofi' I see the activity listed:
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Is this the issue, the activity was saved on the Lead rather than the Customer?
Another way to easier find which Customer recordID it is assigned to: on the Activity List bottom right corner click on the gear icon and add the 'Name' field to the Grid > Update. Now click on the Name it should bring you in a popup to the assigned Customer.
- Mortaza