Unifi mobile will deduct a big chunk of data first and return to you later.

It seems that unifi deducts by 100mb block then return the unused balance later. You can check the unifi mobile app by making a note on your current data balance in the morning, afternoon, night and next morning. You will see the actual balance.

Example ..

balance at 6.22 pm 8/9
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balance at 12.47 am 9/9
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100mb is back to data quota after actual usage is deducted (actual usage is about 3mb)