Hi there!
I cannot say what the problem is without more information, however we have steps here to help troubleshoot login / sync issues:
https://github.com/ankidroid/Anki-Android/wiki/FAQ#sync-is-not-working
-Mike
ログイン画面でアプリがフリーズしてしまいます。--どうしたら良いですか?
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ログイン画面でアプリがフリーズしてしまいます。どうしたら良いですか?