Blocks, like the group or  template part block, render what are called inner blocks. These inner blocks use block list blocks to display ordered content. The trailing inserter is included as the last item in block lists.

When blocks with inner blocks are nested in other inner blocks, the trailing inserter is rendered multiple times. For example, if a template part block is rendered within  a group block, each renders its own inner blocks, which subsequently render two trailing inserters.

One potential solution is to display a single trailing inserter at any given time. We determine which inserter to show by evaluating the currently selected block and ensuring that the trailing inserter is a sibling (that way we're certain they're children of the same inner block)

Co-authored-by: Addison Stavlo <Stavz01@gmail.com>