It’s the relay you joined just before you got the messages. I got the same thing. When you delete the relay it goes away.
nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s not sure if you’re seeing this issue anywhere else but I get a spam message similar to this about every 2 min for the last few weeks. 
It’s the relay you joined just before you got the messages. I got the same thing. When you delete the relay it goes away.
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