Login password requested twice

When starting up my Macbook Pro it prompts me to enter the user password twice. The prompt is displayed as normal over the background wallpaper and upon entering it the bar indicating startup appears, yet once it has completed boot up the background changes (with Catalina it jumps from the night to day image) and then the prompt for the same password appears once more. This is troubling from a security perspective and I see a number of other users have the same issue. This occurred on Yosemite and has continued with Catalina. Some comments here suggest this may be associated with Firevault and/or multiple accounts on one system. This could make sense as I have set up a guest account, although I never use it. However, this does not seem to serve a purpose and any support on how to prevent it or why it occurs is appreciated.