My bibliography set-up relies extensively on BibTeX strings. Until very recently - just now, essentially - this worked fine. Now, however, it works hardly at all.
Here's a minimal example. I'm not entirely sure what the crucial elements are, but if I combine abbrv2.bib with abbrv3.bib, the problem disappears.
\begin{filecontents}{abbrv2.bib}
%:punctuation - but use Biblatex macros where possible!
@string{/ = {\addslash }}
@string{name-some = {Name, Some}}
\end{filecontents}
\begin{filecontents}{abbrv3.bib}
@string{great-stuff = {Great } # / # { Stuff}}
\end{filecontents}
\begin{filecontents}{\jobname.bib}
@article{name-fascinate,
author = name-some,
journal = great-stuff,
pages = {34--67},
year = 1765,
volume = 3,
number = 2,
title = {Fascinating Finds}}
\end{filecontents}
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[backend=biber]{biblatex}
\bibliography{abbrv2, abbrv3, \jobname}
\begin{document}
\autocite{name-fascinate}
\printbibliography
\end{document}
Note the lack of an author in the bibliography entry.
My real document has no authors, journals, publishers, addresses, joining words ....
What is the cause? (Please don't say this is a new feature!) How can I avoid the problem (Can I avoid the problem?) without reverting to BibTeX? Reverting to BibTeX would be a great deal of work, but probably significantly less than doing away with the use of @string.

addbibresource(bibliographyis deprecated), but to no avail. I can't fix it, but I noticed the result depends on the order in which the bib files are loaded. In particular, if I load it "abbrv2.bib", "abbrv3.bib", "\jobname.bib", biber issues a warning "undefined macro "name-some"". So it appears the strings are captured from the immediately previous file ("great stuff" captures the slash), but not if loaded "in chain". Thus, if you merge your abbrv files it works. I know it doesn't help much, but that's what I could find out so far. – gusbrs Dec 08 '17 at 02:56@string, as far as I searched, is not documented in biblatex's manual. There'sxdatathough... – gusbrs Dec 08 '17 at 03:38@stringis from BibTeX and has been recognised in the.bibformat for ... well, ever since I've been using it. Suddenly not supporting it would be a pretty major non-backwards-compatible change. – cfr Dec 08 '17 at 17:22