I'm not sure which component this relates to, so I just put other. Someone please feel free to update if you know the offending component.
For the sake of a simple example, lets say we have a view 'people/owners/%' with default title "Profile" and a Contextual Filter on field "last_name". The Contextual Filter has configuration "Override Title" checked with override value of "{{ title }}". The view is configured so that going to "/people/owners" returns 404, for no results. So, the default "Profile" title should always be overriden, as the view only works when a valid last_name is provided. When we go to /people/owners/johnson, the title is accurately overridden to say "Jeffrey Johnson" on the page. However, the breadcrumb shows "People / Owners / Profile" instead of "People / Owners / Jeffrey Johnson". I've tried changing the Default title from "Profile" to "{{ title }}", but this doesn't work, as I don't believe that field accepts twig input.
I've checked configurations on the Breadcrumb block, as well as the breadcrumb settings in bootstrap sub-theme's COMPONENT >> BREADCRUMBS sections, and don't see anything pertaining to title overrides.
I've searched for similar issues, but haven't found any. If this is a duplicate, I apologize, I must have missed something and would greatly appreciate someone pointing me in the right direction. Or, if this sounds like it's not a core issue, but rather a theme issue, just let me know and we can close this and I'll open a new issue on Bootstrap theme.