Same problem. I've updated one PC and one Dell Notebook. Both with the problem only in the microphone. I had notice that if you enable the resource to hear your microphone (you listen yourself), LX-3000 works. But this is not an resolution.
I experienced the same problem after Windows 10 update. I am on a Lenovo workstation. Trying to use the Lifechat LX-3000 to record voiceover on Techsmith Snagit 18. Techsmith advised that I upgrade to Snagit 19, which I did, but the issue was not resolved. I was told that the driver needed to be updated but there is no driver available for this unit for Windows 10.
I happened upon this fix for myself purely by accident.
I decided to find out which programs were affected by this lack of audio. I have Camtasia 2018 and tried a screen recording and noticed that the audio was turned way down, so I adjusted it back up to 100%. I did a recording and everything was recording properly.
I went back to Snagit 19 and tried a screen capture recording and the audio was also miraculously fixed.
I also use this same headset for Dragon Naturally Speaking (version 13). When I used the Dragon program, the audio for the other programs (Camtasia and Snagit) reverted back to no audio. Again, I went back into Camtasia to readjust the audio input levels and it was fixed.
I am not a tech person so I don't know why it worked or even how it worked... but it is working. Not the most elegant fix but at least, the headset is working in a roundabout way.
It appears to have some conflict with other programs that uses the headset. I am not experiencing any issues with GChat or Skype (as yet).