The mdn web docs the says that column breakpoints are given in the debugger only to function calls:
If the line contains multiple function calls, each one will be given a small blue arrow icon to the left of it. These are called column breakpoints, and allow you to set the breakpoint to happen exactly on any one of the function calls in the line (or multiple calls), by clicking on each relevant one.
However column breakpoints are also set in for loops where no function calls were made. Below is an image i created that highlights the problem:
