I have a symbol within another symbol.
Manipulating elements within the symbol is very slow.
When dragging an element around I observed multiple seconds before the element actually moved to where I stopped my mouse cursor and let go. This made it impossible to align the element against another element. (Leaving Balsamiq for a few minutes to complete another task allowed me to move it quite responsively, but after that move everything slowed down again. It’s like it is updating all the other mockups in the background that use that symbol.)
I have a video showing this in action if required. (And can share the project too.)
Observed on v4.5.3 on a Mac.