When did you update your Seamly? You may do it by clicking the icon at the top of this page or by going to the Help > About Seamly and clicking the link at the bottom left.
However, that may not fix the problem. If you can open the pattern file in a text editor and navigate to line number 690, there’s a line weight that reads “2.0” or something similar. Change it to “2”.
That should sort the problem and prevent it from happening again. If you’re uncertain, you may send me your file and measurements in a private message and I’ll do it for you.