For a couple of months, I've been using 2-3 Amazon Basics manual flashes with Neewer radio triggers on my Canon T4i for focus stacking.
I periodically see the shutter at the bottom of images in the stacks.
When this started I was shooting on Manual at 1/250.
I went down to 1/200 and it became less frequent, but was still there.
I went down to 1/160 and it became less frequent still, but was still there.
I haven't tried to go lower yet, since I needed to recharge the tablet that I use to control my focus rail last night.
This appears to happen regardless of whether the batteries have been freshly charged or not. I already extended the pause time from five to eight seconds for a different reason. Do I need to make it longer still?
Does anyone have any suggestions?