ImageMagick command suddenly stopped working, and webp images not compressing

For the past year or so, I have been using ImageMagick from the command line to batch process png files into webp files - I have been using the commands from here:

Open the folder which you have subfolders containing files with the extensions you want to convert on your terminal.

After that run following command on your terminal:

find . -type f -name "*.png" -exec mogrify -format webp {}  \; -print && find . -type f -name "*.jpg" -exec mogrify -format webp {}  \; -print && find . -type f -name "*.jpeg" -exec mogrify -format webp {}  \; -print

You can also combine all above commands in single expression using regex:

find . -type f -regex ".*\.\(jpg\|jpeg\|png\)" -exec mogrify -format webp {}  \; -print

To remove the leftovers (original files), run following command afterwards:

find . -type f -regex ".*\.\(jpg\|jpeg\|png\)" -exec rm {}  \; -print

I have only been using the second and third commands, with -regex, and then when I tried to use it today, it did nothing (most recently, I used it last week and it worked).

I tried the first command, and it did work, but the webp images are the same size as the png files - it's not compressing them the way that the command was before.

I tested previous png files that I had already converted and compared the webp images and previously I was getting about a 25-35% reduction in size and now I am not getting any from the same source png files.

I have not changed anything in the past few weeks as far as OS updates, adding/deleting anything from the command line, etc. I have ImageMagick 7.1.1 installed on a older MBPro Retina running 10.14.6 Mojave.

I'm not a developer, so I don't know what to do to diagnose anything from the command line, but I'm open to try. I just don't want to make anything worse since it took me some effort to manually install ImageMagick without HomeBrew on my older OS.

Thanks for any suggestions.