What version of yEd are you using (see "Help" -> "About")?
What version of Java are you using (see "Help" -> "About")?
What is your Windows display scale factor (see Windows' "Display" settings option "Make everything bigger")?
What is your Windows text scale factor (see Windows' "Display" settings option "Make text bigger")?
yEd is not a native Windows application, but a cross-platform Java application. (Moreover, yEd uses a fairly old UI toolkit.) Unfortunately, Java does not support all display scale settings equally well and consequently, neither does yEd. yEd/Java applications work well with integral scale factors (i.e. 100%, 200% 300%, ...) and no additional text scaling. Half-point scale factors like 150%, 250%, ... are usually especially bad and result in font sizes like the one depicted in your second screenshot.
In short, use integral scale factors for best results.
However, I am not aware of any changes in this regard due to the latest Windows 10 update. Could it be that you simply changed your display scale factor after your last Windows update?