It might aound silly, but have you looked into a full header of an email which ended up in spam folder?
Normally google provided some info about why and email eded up in soam folder.
I have started using pass (https://www.passwordstore.org) since last year and I'm quite happy with it.
The main advantage of using pass is the feeling that I've control overy passwords and I also understand the process.
If you decided to give it a try, make sure to have a look on available extensions.