For people who reads this stackoverflow question:

There is now a new release of string-grouper: 0.7 which fixes several deprecations warnings and is less prone to Cython build error like the one above as it uses a recent version of sparse_dot_topn package and not the specific dependency sparse_dot_topn_for_blocks.

So:

pip install --upgrade string_grouper

NB: I'm a contributor of this release.