Earlier we had got a big update with Oxygen OS 5.1.7 on OnePlus 6 which fixes the bootloader vulnerability just a few weeks back and we already have another update which might further improve the performance of the device.
The new Oxygen OS 5.1.8 improves the call quality, system stabilization, and also fixes network issues. Due to some bug, the OnePlus team had to pull down the Oxygen OS 5.1.6 and gave the new Oxygen OS 5.1.8 update which company claims to fix the issues faced by Indian users of OnePlus 6.
The new Oxygen OS 5.1.8 also adds DND scheduling feature which was missing on the Indian variants. The new update is just 102MB and will be available in batches and will need to wait for the OTA update to arrive in your device.