I don't see the images in Chrome either. For example for GCV8XG I get the following error messages when loading the page:
Mixed Content: The page at 'https://www.geocaching.com/geocache/GCV8XG_start-hill-sums?guid=56879049-63ad-43c2-ab50-4fdc9db7dc35' was loaded over HTTPS, but requested an insecure element 'http://img.Groundspeak.com/cache/d8e9e836-0798-4c26-b7d7-708560ee0ac0.jpg'. This request was automatically upgraded to HTTPS, For more information see https://blog.chromium.org/2019/10/no-more-mixed-messages-about-https.html
Failed to load resource: net::ERR_CERT_COMMON_NAME_INVALID
So the issue seems to be the mixed content. Additionally the img.Groundspeak.com server seems not to support https. This is something Groundspeak could fix
What I previously did not realize, is that the browser automatically upgrades the request to https so simply changing http->https does not really change anything. I think that using the resolved address for the image could help here. Ie.
https://s3.amazonaws.com/gs-geo-images/d8e9e836-0798-4c26-b7d7-708560ee0ac0.jpg
Unfortunately this does not help with the images you have on other external servers because they also don't support https. Maybe you could approach the provider of those services to ask if they could turn on https support?