Hi, I have exactly the same problem and it also started on June 14th. I found out that it exclusively comes from users with Chinese language from mainly the US, UK, Australia, Ireland, Canada and New Zealand. Therefore, I installed a plugin (CleanTalk) and made blacklists for both, the Chinese language and the country (China). So far, with no success. My site is not US based but it is in US English. I would be grateful if someone has advice! Thank you!