Please check that you do not have referral spoofing turned on. Additionally, check in your Chrome's Developer's network tab to see what kind of errors you are getting.
On Firefox, I'm just getting a bunch of 403 errors when the GET request is sent to MangaDex's image servers but can access the images themselves if I go to the link, also, it happens randomly, works on some, not on others, and on some it doesn't work unless I reload, some it doesn't work even if I reload, it's just random.
I was having the same problem for every chapter older than a month or so. Eventually I drilled down and figured out the issue: there's a script that needs to run hosted on mangadex.network that NoScript may not list initially. Click one of the "click to reload" images a few times and it should show up in NoScript, then allow scripts from mangadex.network and reload. That fixed the issue for me.