What percentage of users have completion issues in your LMS, assuming the course works correctly?

Even if you do all these things, there seems to be a certain error rate. We just rolled out a long course to 30,000 people and only had 50 have a true problem (not user error). In a previous LMS with another company, they didn't see a need to troubleshoot when we'd have 50 people out of 1300 with an issue. We discovered some fixes like using SCORM 2004, deleting unused variables, avoiding resume state on slides with a lot of layers/states, etc. It is still odd that in some cases random users seem to have firewall issues maybe while many other people are just fine. This just may be one of the mysteries of life. ;)