I was very enthusiastic about LS until our client happened to stumble upon the following stange behaviour.

1. Created a small test survey (2 groups, 5 questions) and invited 1 participant from client organisation. All went well, no problems found
2. Created new survey; 22 groups, 47 questions, anonymized, closed, no date stamp nor ip-address nor ref-url logged, no cookie set, no assessment, no token-based persistence; activated and invited about 150 participants
3. Few people arrived at the last page, others were dropped back to base-url (i.e. surveys list)
4. After 1,5 day, out of 60 total responses, only 18 were completed. 5 individuals got in contact with me that they had repeatedly tried to fill in the survey and quit after 3 to 5 attempts.
5. Halfway the first day we activated debug mode - participants reported no debug statements in the pages
6. Participants were kicked out at various pages, some as early as the first page, some at the last page and everything in between; confirmed when looking at the survey results.

Some notes:

1. We checked the apache logs but didn't find related issues (errors reported missing favicon (repaired) and 'PHP Deprecated: Call-time pass-by-reference'; furthermore some errors such as 'PHP Notice: Undefined variable: sid in /var/www/admin/access_denied.php on line 73' (admin.php as referrer hence irrelevant) and 'PHP Warning: Invalid argument supplied for foreach() in /var/www/common.php on line 4905' -- nothing to get excited about
2. Customer was using proxy to connect from, i.e. all 150 had identical ip-addresses and routes
3. Checked Suhosin extension for Apache; installed but not running. Still, specified larger variable values (2048) but php-info() doesn't show any reference to them or suhosi, as expected
4. Platform has been used before without any problems; Survey size was smaller (two groups, 10 questions), total participants roughly equal

This is bugging me now for 2 days and I'm growing both desperate and furious since I don't have a clue to even start diagnosing.

Configuration:

• LS: Version 1.90+ Build 9642
• LS: Session life time 3600 (confirmed - I triggered a session time out)
• LS: XSS filtering active
• Ubuntu 10.04.2 LTS
• PHP Version 5.3.2-1ubuntu4.7
• Apache/2.2.14
• Apache2 default values
• Max Requests:: Per Child: 0 - Keep Alive: on - Max Per Connection: 100
• Timeouts:: Connection: 300 - Keep-Alive: 15

Any suggestions??
Thansk in advance!
Paul