I have two similar, but completely separate issues when attempting to edit recorded game footage.
Footage captured using Shadowplay/GeForce will edit, playback, and render visually without issue. However, the audio will play normally for a few seconds before glitching out. At best it will sound like garbled glitching, at worst it will sound like a quick burst of mic feedback. It will then resume playing properly for a few more seconds before repeating. Even once exported, it will still sound exactly like it played back.
Footage captured using an Elgato HD capture card is even worse. Once again, so long as I'm using only the video it will work fine. However, I cannot even attempt to playback any audio captured this way. If it's connected to the video, or separated and the video removed- it will freeze the editor for several minutes. Then the editor will play back blank audio- nothing plays. That will play for about a second or two, before freezing again. Attempting to export this audio/video without playing it back will also result in perfect video and completely silent audio. Attempting to generate the waveform for the audio will lock up the editor for an indefinite period of time- I gave up and used task manager to quit after 3 hours. (I was attempting to generate the waveform for a 5 second clip.)
As I said, the video works perfectly from both methods of capture, and audio that was either an MP3 that never had video attached, or was captured using a video camera never has this problem. I have tried changing all sound settings I could find using the Help menu and googling the problem, but nothing helped. I have also tried turning on "automatically create proxy files", changing the audio sample rates, and changing the video settings themselves. The sound does exist and works perfectly well when playing back the captured footage using video players however.
All of this is on Magix Edit Pro 2016 Plus. (steam version, if that makes a difference) I have downloaded no extra files or plugins that I know of.
My computer has an intel(R) Core i5-4460 CPU @ 3.20 GHz, 16GB of ram, 819GB free of 1.81TB, and is Windows 10.