Check with composer update/install -o -vvv whether the package is being loaded from composers’ cache.
If yes, try clearing composer’s cache or try adding --cache-dir=/dev/null.
To force downloading an archive instead of cloning sources, use the --prefer-dist option in combination with --no-dev.
Otherwise you could try raising composer’s process timeout value:
export COMPOSER_PROCESS_TIMEOUT=600 # default is 300