Are you sure the problem only happens during scenes with lots of panning or camera movement? Is so, this leads to the conclusion that enois is making: It is a problem that was caused when the tape was recorded and is not
a playback problem. As stated, this happens when the drum speed is not constant during recording which can be caused by the motion of the camera during shooting. It probably happens to some extent even on typical "consumer shot" video, not just on really fast pans.
Why it should happen only on your Digital8 tapes is confusing though your analog tapes were made on a different camcorder (D8 camcorders cannot
record in analog mode).
Anyway, if this was a "record time" issue, then the defect should always happen in the exact same place on the recording every time you play it back. If you can confirm this, there may be nothing wrong with your camcorder. If instead, the problem is occurring randomly at other places in the recording, especially in scenes where the camera was held nice and steady, then it is more likely a playback problem with your camcorder today.
This is a bit of a stretch because your specific problem is a bit different that the ones I've seen fixed (on YouTube), but there is one thing that you can try that might (temporarily) solve the problem. Its going to sound crazy but, with the tape removed and the camcorder off, hit the bottom of the camcorder a few times with the palm of your hand (watch the videos linked below first). It just might fix it. Sony 8mm camcorders are notorious for various connections inside "going bad". It is thought to be corrosion of the mating surfaces in the connections, usually a ribbon cable connection to a circuit board. By tapping the camcorder, the cable wiggles around enough relative to the board to displace the corrosion and reestablish the connection.
Check out these videos:
These show how the how the hitting or tapping the camcorder "fixes" problems:
This one shows how the problem should be fixed more permanently:
Note how many ribbon cables there are, all of which can have connection problems. Note too that your camcorder has to properly sense that the tape is digital or analog and then adapt, changing the speed that the video head spins at and the speed the tape moves across it (both higher for digital). This might
account for why it can work for analog playback but not digital.
Obviously, try at your own risk, and there is no guarantee this will fix it, but it seems quite possible.
as they say, YMMV.