My interpretation is that the error is that the blockquotes are not styled as expected, unless the class is applied.
I’m not into Bootstrap, but it seems adding the class would fix it, though it seems redundant IMO to have to put a blockquote class on a blockquote element.
If there are thousands, it could be a lot of work, though many editors do have a “search and replace” function which may help.
Though what I might do, with my non-conforming to Bootstrap ways, is to go in the CSS and override the reset that removes the blockquote styling and add:-
blockquote {
/* Style as I want blockquote to appear */
}