Certain Clips Get Desynced When Imported?

I've been having a problem since I installed Premiere Elements with certain clips. It seems to primarily be with longer clips, although it does occasionally happen with shorter clips. It may have something to do with file types or codecs, since videos of certain file types don't seem to have these problems, but multiple file types have had the same issue. I don't know exactly how to describe it, the videos run fine normally, but when imported into Premiere Elements the video, but not the audio, suffers occasional glitches and hiccups.

Points in the video will skip back a few frames, while the audio keeps running forward as normal. Oddly, despite it usually showing up in longer videos, it shows up even in the first few minutes of those videos. These glitches can occur several times a minute, and while they are only a few frames of desync each time, the errors are so frequent that it is virtually impossible to maintain audio consistency throughout the video.

Note that this isn't just a playback problem, the exported videos have these glitches. Even if I don't include any edits, simply importing a file to a project and then exporting it as a movie causes the massive desyncs to show up. There doesn't seem to be any way to fix the problems, except for manually, which is obviously not an option.

I also occasionally have a problem where moving a section of the clip one frame or moving it to a different layer causes the video to jump slightly, changing the point in the video it comes from. I imagine it has the same root cause, but I have no idea how the two problems are connected.