Thumbnails from cards containing images in low resolution. How do I fix this?

In summary:

• I have been using Trello for years. Recently I noticed that new images (digital paintings I sell and display on Trello cards) are always in lower resolution/blurry compared to the old images I uploaded previously.

I tried:

• Different browsers, mobile and desktop. Images are still blurry.
• Checking image size in pixels and dimensions on Photoshop. All images are saved to standard HD (1920px on the larger size of the image, either height or width)
• Re-setting zoom size of the browser to the standard size.
  
  

For reference: I downloaded a painting that was previously looking very sharp and HD from an old card and re-posted it on a new card. The image is now blurry as well. This implies the issue is on Trello, not my browser or image resizing habits. 

I fear I might have to leave Trello and use something else if the thumbnails are low-resolution from now on. I hope not! Thank you in advance for anyone reading.