My experience with 10.14.3 beta can be summed up as, I've spent the entire evening, from 6pm to 6am, trying to get the Internet connections to work -- Wifi, ethernet, and so forth -- without solid success. Each time I've tried to configure one communication modality, another stops working. Either an Apply command wipes out the existing settings or Wifi channel 2 supersedes Wifi channel 1 or the ethernet connection is unrecognized.
I'm not exaggerating, this has been my worse setup experience with an Apple OS in recent memory. Over on the public forums the answer most commonly proposed and implemented has been to uninstall Mojave and reinstall High Sierra, which most remember as working flawlessly. tt didn't, but it was easier to setup and more reliable than Mojave so far has been. That's a sad situation!
If others here aren't having these problems -- which is entirely possible, given the greater expertise available -- what worked for you? I'm BOUT ready to downgrade to High Sierra, too, but if you have had problems and then surmounted them, I'd be glad to follow in your footsteps. Thanks for your thoughts, assistance, and reassurances that this won't become the norm for Apple beta releases.