When the image in a post isn't HD, it just keeps trying to load, so the load icon just keeps spinning. Trying to download doesn't work at that point either.
Toggling HD off fixes it, the loading icon disappears and you can download no problem.
Could it default to non-HD at some point once it's clear it's not HD?
Here is a example post: https://piefed.social/post/1877758

And here a video showing the issue, bit long at 51seconds:
https://files.catbox.moe/kywene.mp4

Thanks for your hard work, amazing app.

Same issue on my end

I know the button says "HD" but what it actually does is toggle between the post thumbnail url and the source url.

Usually the thumbnail is a compressed version of the source url in cases where the source url is an image. The thumbnail URL is typically hosted on your instance whereas the source URL can be from anywhere.

For example, you see a funny image from Imgur so you grab the link and post it to piefed.social. Piefed.social generates a thumbnail image and stores it on the Piefed.social server.

Summit will use the thumbnail when the image is small (eg. in the post feed) but when you are looking at the full post, the app prefers the original image over the thumbnail although it will fallback to the thumbnail. This is done because typically the thumbnail is a downscaled image of the original (so it's much much blurrier).

In the video you can see that Summit has loaded the thumbnail and it's trying to load the original.

Now because the thumbnail and source image can be hosted in different places it is entirely possible for the thumbnail to load but the source url to not load or vise-versa causing this issue. In my opinion, this is not a fault of Summit, it's just trying to give you the best possible experience and the best possible experience is to show you the full resolution image when it can.

That being said, your video shows there is a gap in the app. When you expanded the image from the post, it doesn't allow you to toggle to the thumbnail image. This is something that I will fix in the next update.

Thank you for your thorough explanation and for all that you do.

Hey boss, I don't know if this is related, or just a problem with my device, so I'm just posting a comment here for now. The following has been happening with various posts at least the past few days.
Why wouldn't the image show up when I tap it? It's right there, even if it's not the "HD" version.
Here is a short video: https://files.catbox.moe/13sr3t.mp4
And here is the post if that helps: https://piefed.social/post/1919090 (here is another post with the same issue if it helps https://piefed.social/post/1919095)
Edit: also, while I have you, should I do something with the post title, [ISSUE]? Not sure if you want them to be a certain way.

What version of the app are you using?

Sorry, I should have checked that first. I was on 1.80.2
I updated to 1.80.5 just now and cleared the cache. The image loads, that error message still appears over it, but I can now push the "HD" button and it goes away, so all good, sorry for wasting your time!