In both, I clearly see a bright spot on the southern side of the disk. Obviously, if it is something in the imaging train, it would be there for both. But if it were an artifact of processing, I'd think only one would have it.
Anyway, the imaging details: 15" Newt at approx 3900mm EFL. Baader IR685 Pass filter. ASI120MM at 100% gain, 0.162s exposures. For the posted image, 2774 frames were collected and this is a stack of the best 80% using a single reference point and noise robust 6 in AS!2. The stack was sharpened with slider 6 in registax 6 and then final processing was carried out in photoshop.
Triton is clearly visible where it should be. The image was recorded for 525s starting at 0503UT. WinJupos puts the CM of Neptune for this capture at 346, although the spot is clearly not on the CM.
So, it looks to me like I captured a bright spot. However, after several years of doing this, I'm not expert enough to know if this could be some sort of artifact and, if it is, I'd very much appreciate being set straight before I get too excited.
Here is the stack from the first avi (at 0503), fully processed. I'll follow with a crop and enlargement. Then a shot from the second avi.