ratelimit message is incorrect.
In 5c596cdbc086698c52 I added an XXXX comment to rate_limit_log.
When we say "100 messages suppressed in the last 3600 seconds", we're not being accurate. Those messages were suppressed over a period of time at the start of which the last message of this type was logged, and ending some time before the present... but they could have occurred days ago, or all 1 second ago.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information