Thanks. But why this is related to interval ramping?

As I mentioned, with exactly the same camera parameters (shutter 1/60, 1/8; ISO 200; Aperture f/4), and even with the "Release Time" being set to 200ms in the timer, I was able to do a regular TL successfully with a much shorter interval of only 1 sec.

As we started this thread, the missing shots issue was seen when doing interval ramping without HDR in the field. But I haven't find a means to reproduce it. The HDR setup is the easiest way to produce this issue within 100 test shots.

Could it be possible that the timer's 'release time' might be shorter when there's an interval ramping?

Thank you!