IDE app font formatting (1.8.12 Windows) just blew up

I've been copying sketches from the Arduino site and pasting them into sketches. Seemed to be going fine for quite a few. Then suddenly today - for no apparent reason - the font sizes in the sketches blew up. Lots of huge fonts mixed with smaller. It's all over the map. Strangely, the sketches compile, but the IDE is essentially unusable like this.

Help.

Lots of missing information Jim.

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No idea what causes this or how to solve the root cause.

What happens when you paste the copied content first in a normal editor (does it look normal in there?), next cut it from there and paste it in an empty sketch?

Everything works fine online. But with the Windows IDE, every sketch (including New) opens with gigantic fonts and no way to change it.

You can try the following; never used it.

In the IDE, file -> preferences.
2)
Near the bottom is a link "C:\users...." under "More preferences can be directly edited in the file"
3)
Click it and it will open Windows Explorer with the directory where preferences.txt is stored.
4)
Close the IDE
5)
Make a backup of the preferences.txt
6)
Open preferences.txt in your favourite text editor.
7)
Search for font
Mine is

editor.font=Monospaced,plain,12

8)
Adjust font if it looks odd.
9)
Save the file
10)
Start the IDE and check.