I no longer subscribe (and the links are broken to me) but when I did it was (confusingly) separate logins. It appeared to be the same but I found the site login would need periodic refresh while the forum login stayed locked and logged in all the time.
Thanks Mike, I've encountered similar login status variation across the site (and it seems there are 3 logins: site, forum, and forum-subscriber, and I generally use the latter). I've seen that both before and after I became a subscriber.
In any case it seems to me that the subscriber status doesn't matter for the broken attachment links. There is something else going on. You, I, and apparently now David, all encounter broken attachments (pre-Nov 2019 in my case), and that covers both subscribers and non alike.
I guess I'll hunt for a "webmaster" contact somewhere... I posted here because I couldn't find a contact help/support option for the forum, so I figured this must be where people report forum technical issues. (Edit: just sent an email to the customer service address shown on the main website page...)
For info, which browser and OS are you using?
Thanks