There is composer/, module/ and pimple/ in the vendor directory of this link https://extdist.wmflabs.org/dist/extensions/Flow-REL1_31-a7bc00b.tar.gz, but composer/ and pimple/ is missing in this link https://extdist.wmflabs.org/dist/extensions/Flow-REL1_32-bf651cf.tar.gz
Eventually, I am given below error:
PHP Fatal error: Class 'Pimple\Container' not found in /mywikis/installation/path/extensions/Flow/includes/Container.php on line 5
... and cannot access or use Structured Discussion pages at all, before I executed manually composer install --no-dev in the extensions/Flow directory.
UPDATE I am encountered same problem in TemplateStyles of REL1_32