Why does the wallet keep locking?
まだ日本語では提供されていないため、原文で表示しています。上のメニューから翻訳できます。
The wallet locks after one hour without use. Time the app spends in the background counts toward that hour. It also locks whenever your phone closes the app to free memory, because the unlocked state is kept in memory only and is never saved.
Locking does not change anything in your wallet. Unlock with your password or Face ID and everything is as you left it. You can lock it yourself at any time from Settings.