2nd Merge broke the first Merge

For some reason, a second Merge in my flow broke the effect of the first Merge. Here is a screenshot. In the meantime, I rendered out the shot with the 2nd Merge disabled.

Can someone explain to me why a Merge would break a previous Merge in the flow?

Thanks in advance.

Maybe the Tracker node is set to BG Only?

Maybe the Tracker node is set to BG Only?

I switched it to FG Only and that fixed it. Now, I understand the Tracker node better.

Thanks for your help.