Instagram Reel looks good on my account but blurry on another account — what is going on?

I'm having a frustrating issue with an Instagram Reel I just posted.

The source video is high quality, and when I view the Reel from the account that uploaded it, it looks sharp and clean. However, when I view the exact same Reel from a different Instagram account, the quality looks significantly worse, especially in the feed. It appears blurry and compressed.

Some additional details:

• Shot with Blackmagic Cam on iPhone, edited in Final Cut Pro.
• Exported as a vertical Reel (1080x1920), H.264.
• The Reel looked good immediately after upload on the posting account.
• The issue is specifically that the same Reel looks worse when viewed from another account.
• I've confirmed that I'm looking at the exact same post.
• The difference is noticeable enough that it feels like two different quality versions are being served.

My questions:

1. Is Instagram known to serve different quality versions to different accounts?
2. Does Instagram take time to finish processing higher-quality versions after a Reel is posted?
3. Could this be a caching issue on the viewing account/device?
4. Has anyone experienced a Reel looking great on the uploader's account but blurry on other accounts?

Any advice or troubleshooting steps would be greatly appreciated. I've spent a lot of time getting the video looking right, so it's frustrating not knowing whether other people are seeing the high-quality version or the blurry one.