Nevertheless, I had my Hive keys as a document on my phone and I feel that the hack may come from there or perhaps because my Hivesigner password was saved on my chrome browser, which allowed the hacker to access the password somehow. I didn't lose much but it wasn't a good experience for me.

Both of these are bad practices. You should not keep any keys on the phone. Nor saved in the browser.

As you say: time to improve your security.