OxygenOS 11 Open Beta 3 started rolling out to OnePlus 8 and 8 Pro devices almost two weeks ago.

However, based on recent community posts in the OnePlus forums, an OTA to a stable build of OxygenOS 11 from the OxygenOS 11 Open Beta 3 has been completely wiping away user data on some OnePlus 8 and 8 Pro devices.
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https://www.androidcentral.com/oneplus-88-pro-oxygenos-11-open-beta-3-wiping-away-user-data