webpack: Compile stuck at "additional chunk assets"

After updating to node v4.1.2, I’m seeing my production compilation take much much longer. I think it took around 40 seconds before, and it now takes about 4 minutes. I tried updating from webpack 1.4.13 to 1.12.2, but didn’t seem to change anything. I added the ProgressPlugin, and the compilation is hanging for minutes on “additional chunk assets” at 79%. If I remove the UglifyJsPlugin that wait time is gone, similar to this issue: https://github.com/webpack/webpack/issues/537 . I tried sourceMap: false in the Uglify plugin but that doesn’t seem to help.

Also, is it usual for the percentages to not always increase with the ProgressPlugin? I’m seeing percentages go from 25->26->27->28->27->26 and then back up. Is that normal? That part’s not a huge deal, just weird.