The way lights are computed in Sweet Home 3D didn't change in version 2.4.
But on the contrary, they did change in the Advanced rendering plug-in version ≥ 1.2 you seem to use. As explained here, I enlarged a little lamp lights to soften shadows, and maybe this change was great in your case.
May I suggest you to add additional lights in you plan?
db4tech created a nice SH3F library containing various lights described here.