Recently, I always got HTTP 417 when /memo/wait-submit. I have wrote a cli utility to temporary solve this problem. It seems that some failure still occured on my account @memo
Looks like a few transactions from a week or two ago were broadcast but never got mined for some reason. They were in Memo's DB but not on-chain.
The normal solution would be to rebroadcast the old unconfirmed transactions so they get mined correctly and then can use their outputs on new transactions.
But it looks like you have spent the outputs in a separate new transaction. So the old transactions would be double spends and can no longer be rebroadcast successfully.
I've deleted the old unconfirmed transactions from Memo app's DB (there were 7 of them). Your account should work fine now but a few previous actions got removed.