Device: PC 64bit
OS + version: Windows 10 Pro 19042.867
Browser + version: Chrome 89.0.4389.82; Firefox 86.0.1; Edge 89.0.774.50
Whether you've got any adblockers/script blocking/anything unusual installed as a browser add-on: only on Chrome; Mangadex is whitelisted in all of them, but I still turned them off, with the same result
If you're using an ISP with a history of blocking things: no
Have you switched your DNS servers: no
If you've tried a VPN: no
Have you tried MD in an incognito tab: yes
Have you tried MD in a different browser: yes (Firefox, Edge)
Have you cleared site data/cookies for MD: yes
A slight correction to my previous post: it's not that I can manually download images from older chapters, it's that I can manually download any images (at least in Chrome and Edge), but .jpgs save as .jfif (they can be renamed and work correctly), while .pngs work just fine.