I don't know if you have faced this issue or not but recently I was suffering from this issue. Last week I was doing the setup of my Yahoo account in Outlook 2016 and after set up when I opened my Yahoo account in Outlook, then I got to know that my inbox was not fully synchronized and a few of the folders were missing. Then, went to Google for finding an effective solution to this issue. After few minutes, I found this amazing article that explained how to set up Yahoo mail in Outlook 2016. After going through this article I realized that my Yahoo account was not properly set up in Outlook. This article helped me in setting up my Yahoo account in Outlook 2016. Additionally, this article also provides the step-by-step procedure to set up a Yahoo account in Outlook 2019.

Furthermore, if you want to secure your Yahoo data or you need a professional software solution to import Yahoo Account in Outlook, then this article discussed an effective utility called Cigati Yahoo backup tool. You can try its free demo version to analyze its performance.