Some Data is lost when it submit

Dear torro form team;
I use torro form to collect data from users..
I give access to all members of site ,, users first register in the site and then fill the form.
my users is above 1000
my form had 5 pages, my problem is that i found some users results empty ,, also some of them have one page empty (first page) ,, and some had 2 pages empty(first and second)
between every 10 users i found one or two with this problem ..
please can you help me to know what is the problem ?