This is a known glitch, as I posted about in the other thread that you also posted in.

I doubt Khan Academy will remove the rate limit, since that would leave it open for bots to spam the discussion area with thousands or millions of comments/day.

If you want to help Khan Academy figure out what is causing the problem so they can fix it, there is information you can give them.  Please see my post about it; I tagged you in a comment under the post.

My post is here: https://support.khanacademy.org/hc/en-us/community/posts/35231517036813-Is-anyone-else-bumping-into-the-rate-limit-for-posting-even-though-posting-fewer-than-100-times-day

(Khan Academy will probably hold this comment pending approval since it has a weblink, even though it is to their own website.)