I work with a fingerprint scanner almost daily, and have seen literally thousands of fingerprints and can tell you definitively that it is the technology that's lacking, not you! True, yes, that there are many people that have very faint fingerprints, if any at all. But the technology not being able to handle these anomalies is what's frustrating. So if they've dialed up the sensitivity, or number of reading points, then all they are doing is increasing the number of people who will have issues.
The real problem here, as you have highlighted, is not really even the technology. What needs to be happening is better training for the CMs to handle situations when the scanners just aren't able to handle someone's fingerprint now that they are more sensitive. They need to be blaming the machines, not the guests! A very simple, "On no, I'm sorry it's giving you a problem. Let's see what we can try to do to get it to work." Or even throw in a small bit of new information, "Very sorry it's being so fickle. Ever since we upgraded the machines they have become much more sensitive and seem to give a lot of people some problems. I appreciate your patience while I try to get it to work for you."
Super simple. All it takes is how it's worded that can make the frustrating situation a bit more bearable. No need for flaring tempers from the CMs. That's their number one job, extraordinary guest service.
The times are a changing, so if they can't stand the heat then they need to get out of the kitchen!