I am having the same exact problem that was described in this WordPress.com support forum post from a couple years ago: All of a sudden, I can't comment on blogs that I have been regularly reading (and commenting on) for a while.
From what I gathered from lessepea's earlier forum post, I need to have Support "unspam me." A couple members posted that it seemed like a random Akismet problem.
It just doesn't make any sense, because I've been commenting on these blogs for a while now with no problem - now, when I type and click "submit" on a comment, the page re-loads (which makes me think that it worked) but then my comment just doesn't show up! (And these are blogs that I know do not require comment moderation first.) If I copy and paste what I typed before to try again, I get a "duplicate comment" message - but my comment still doesn't show? Please help, so frustrated :(
The blog I need help with is www.prayersandapples.com.