That's the problem with maillon rapide screwlinks - they're not designed for situations where they're jiggled about, as there's no spring tension trying to keep the sleeve closed. Once the initial bite is lost, they unscrew all by themselves. I've had it happen to me many times in caving, where we use them to join the front of harnesses together. It's killed a few of us. I know some people try to stop it by spannering them incredibly tight or using thread-lock compound, but that's not permitted by the manufacturer - see http://www.peguet.fr/gb/peguet-documentations.cfm for the official torque values, typically 4.5Nm for the sizes on lanyards. Cranking them tighter damages the sleeve and can potentially weaken them to a dangerous level, as unlike with a karabiner the sleeve is a fully-loadbearing element. Peguet make the point that the user has to verify the correct torque as part of every pre-use inspection, which 99% of users won't even know they should, never mind bother to or have a torque wrench handy. Without one, they're breaking the law by not correctly using category 3 PPE. The sensible approach is to throw them away and use a karabiner instead - twistlock or triple-lock gates are just as strong, far easier to check, and will always snap closed if anything rubs against them. Historically a number of the big utility companies went with maillons because they thought it'd make lanyards safer (not because of the staying-closed thing, but because you can load them in any direction) - however it's caused more problems than it ever solved. Yes, your user should check more carefully - but even if they do, it's just as likely the maillon would come undone during the working day when they can't see it.