Yeah, it's a DDoS... it has been going on for awhile - not sure how long . Likely existed previously, but may have been introduced or amplified/made worse after mucking around w/ the block submissions and drift time.

How are they performing it exactly? It would be easier to see if I had a node setup, but don't. But, there are probably several known methods that could be used. Notice the connections completely drop to 0 at the same time as the difficulty levels.. The honest nodes on the network are being isolated/cut-off.. Notice all the complaints of people saying their Electrum wallets won't sync? Maybe not because anyone complaining of it on a forum or wherever has their post removed, or is given an intentionally wrong answer as to why their wallets won't sync-up. Don't even get me started on the QT Wallet.

Either way, it's not good and I'm not sure what (realistically) should or can be done at this point. One thing is for certain, I don't see any urgency whatsoever from the Dev team to address this.