I/soft webform not displaying members details

I have a webform hosted by i/soft that does not allow some of my members to see their own data from a link in an email. It is intermittent but we have had about 300 members say they can not see their data.
Any ideas as to why – and what to do about it more importantly

There was a known issue from the end of March until April 1 where parameters were not feeding in links. It is on the known issues page. That could have been what caused it.