Make "All" the default inbox function
I missed an important email which could have cost a lot of money. Fortunately I saw it on my phone but it was not showing up on my PC's inbox. I realised that my inbox had "primary" selected as default and this email along with many others were not showing in the inbox. Once I realised what the problem was I changed the default to "all" and my issue was resolved. However I had not set it to primary in the first place and so it must have been set when Yahoo upgraded. You really should change this so that the default option is "All" unless the user decides to select "primary".
We encourage you to read at the top of the Uservoice header (forum). There we provide What’s New, Coming Soon and some Tips. There we mention how to disable Inbox Categories: All, Priority, etc. Definitely read those as we update them with useful information. Thanks.
https://yahoo.uservoice.com/forums/962180-new-yahoo-mail