After some confusion, OnePlus says there's nothing to worry about in its kernel.

A few tidbits of information swirled yesterday about the Nougat update for the OnePlus 3 and 3T in regards to what kernel it was using. Looking at logs, some users had found messages indicating that the OxygenOS 4.0.1 build was using a debug kernel in what would otherwise be completely release-level software. With a debug kernel, unknowing consumers would be vulnerable to various attacks, as there would theoretically be no checks against modifying the system folder of the phone.

OnePlus 3T

Thankfully, OnePlus has confirmed to Android Central that this messaging was an error, and the OxygenOS software is indeed running a proper release kernel to match the consumer-ready software running on the phone. The debug message found by some users had been triggered instead by the use of common Systrace tools, which gathers performance information about the system — the kernel, in fact, is a proper release version and not a debug kernel.

This is the case for both OxygenOS 4.0.0 and 4.0.1 builds, and OnePlus says that it plans to remove the debug information and warning generated by the Systrace tools so there isn't any future confusion. Without deeper analysis we have to take OnePlus at its word here, so right now we can call this a bit of sloppy log management rather than a detrimental kernel development issue.