The OnePlus 5 and 5T have been updated to OxygenOS 9.0.5, a software update that raises the 2017 flagships' security patch level to April 2019. It also addresses some problems with calls in third-party apps reported by users. This update also makes the first-party phone app more stable.
https://www.notebookcheck.net/Latest-stable-update-for-OnePlus-5-5T-brings-April-security-patch-fixes-some-things.419710.0.html