I have a AVT 8710 as well as an ES10 which did not fix this problem. What is the problem and is it fixable?

Thank you.

Thanks for he image. The defect looks like dropout. But you need to tell us more. How is the tape being played and captured (what VCR? What capture device?). Does it appear in multiple images, or all the time, or on and off? Does it appear when played on a TV? Is it always in the same place in the same frames? Does it happen on other tapes?

It can be caused by damaged or dirty tape, dirty or damaged video heads, electronic failure of VCR circuitry, etc.
No, a tbc wouldn't fix this. It could be possible to do so, but it depends on your answers to the questions.

The vcr is a Sony tvr-128. The tape is an 8mm. The capture card is an ATI 650 USB. The problem only appears once in the whole tape. The problem does not happen on other tapes.

Thanks for the info. By "once" do you mean it's only 1 frame? If only one or a very few frame it's possible to repair, but we would need a short section of the original, unprocessed capture. The image you posted has been resized. You need VirtualDub in "direct stream copy" mode to make a few short sections of unprocessed AVI that you can post in the forum. You will need Avisynth for repairing.

If this is Video8/Hi8 (not Digital8), it's likely an alignment error on the original camera, and cannot be fixed.
Or a bad tape, or a bad section of tape.
Exactly when/how it appears will narrow down the issue. But it still won't fix it.

It's not video heads, dirty, etc, as first thought. It's not VHS. Sony 8mm tapes are special in some ways.

If the damage is only 1 or 2 frames, it can often be repaired using one of Avisynth's MC motion interpolation filters. But if more frames, fast motion, camera jiggle, etc., forget it. Can't draw conclusions from a single image.

Many will cut a few such frames for a final video, which I've seen often, and the original video gets archived for its personal value.