A handful of language learning apps mysteriously disappeared from popular Android app stores in China — the apps, including highly popular ones like Duolingo and Memrise, appear to be the target of a new education policy China has adopted, which bans students from learning from teachers based overseas.

According to a July report from the South China Morning Post (SCMP), China first adopted the policy last month to crack down on off-campus tutoring — the policy bans tutoring on weekends and holidays and also does not allow educational technology companies to raise capital through initial public offerings. The policy also bans overseas investors from investing in certain education firms that teach school curriculum, according to the SCMP.

A little less than a month after finalizing the policy, the SCMP reported on Aug. 6 that the language learning apps have disappeared from most of China’s app stores, though there is some inconsistency as to which apps have been removed and where (for example, Duolingo was removed from the Huawei- and Xiaomi-run Android app stores, but remains on Apple’s iOS app store). Duolingo released a statement to some media outlets addressing the app’s disappearance in China, noting that the Pittsburgh-based company views China as a very high-potential market.

“We are working to address the issue and are hopeful that the app will be reinstated in the near term,” Duolingo told Reuters. “In the meanwhile, existing users in China can continue to use the app as they always do.”

The disappearance of the apps is somewhat suspect for numerous reasons, as the SCMP notes — first, the apps in question disappeared with complete silence from the Chinese government. Although the government has been fairly vocal about the new education policy, it has not said anything specifically regarding language learning apps. Additionally, the apps involved largely involve automated learning — while they are developed and run by overseas companies, they don’t involve teachers, per se.