scrapy crawler is called through a shell script, which is used as the command line in a crontab entry. The shell script looks like:
scrapy crawl targethost.com
when time is due and it did execute, but seems only the constructor is called (I verified with debug output). The problem is solved by re-write the shell script as:
scrapy crawl targethost.com &> cronlog.log
I just don't know why.
Scrapy executes correctly, but doesn't output all its messages to STDOUT, so the simple pipe (>) doesn't redirect everything into your file, only that stuff that goes to STDOUT (which as you say, seems to be the constructor only).
With &> it fetches all messages from scrapy and puts them into your log.
scrapy script called from cron only constructor called