@mattches No. I don’t alter the default Shield settings unless I’m having a specific issue with a website that seems like it might be related to the settings (like when phone calling from GMail wasn’t working because Shields were ‘UP’).
As for Yahoo! Mail’s own settings, I’ve checked those and haven’t seen any that appear relevant to the issue. Do you know of any?
The only setting I see related to images is “Show images in messages” (under “Viewing email”), which I have set to the default: “Always, except in spam folder.”