According to a post on the OnePlus forums, the company stated that they had originally planned for the update to reach all of its users in 48 hours. However they later updated their post saying, “Due to some reports of issues while upgrading, we are temporarily stopping the rollout to investigate. We will start back up as soon as possible.”
Unfortunately it is unclear as to what these issues might be as the company did not share them, so for now OnePlus 3 owners who did not get the update will just have to wait. As for those who already received their updates, we’re not sure if this has affected your devices negatively as there haven’t been any reports of major issues.
It is possible that maybe OnePlus has heard about how their updates have exposed the IMEI numbers of their OnePlus devices, and are looking to correct that before other handsets receive their updates. Either way we’ll just have to wait and see.