Compact after $unset

I’ve got a 3-member replica set. I ran

db.mycollection.updateMany({}, {$unset: {uselessField: false}})

Then

db.mycollection.stats().freeStorageSize

shows about 7gb free.

But

db.runCommand({compact: 'mycollection', force: true})

gives bytesFreed is zero

Is there a way to reclaim data removed by $unset?

You have to contact to MongoDB contact may, they can help you.