On Sat Nov 14 2020 Lars Ingebrigtsen wrote:
> > -  (let ((end-field (copy-marker (bibtex-end-of-field bounds))))
> > +  (let ((fill-prefix
> > +	 (make-string (+ bibtex-entry-offset bibtex-contline-indentation) ?\s))
> > +	(end-field (copy-marker (bibtex-end-of-field bounds))))
> 
> This patch would make it impossible for people to alter fill-prefix
> (from the mode hook, for instance), so I don't think this is the right
> solution.

Can you please try the attached patch using hack-local-variables-hook?
This was partly inspired by the related comment

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21764#15

which had somehow escaped my attention.  The issues mentioned in
this comment should likewise be fixed by the attached patch.