As Peter mentioned, just get the Makita black rubber strips.
In my personal observation, I believe the failure cause is the relatively high linear thermal expansion of the aluminum rail. The clear plastic Festool strip is way more rigid than the Makita black rubber ones. As the rail expands, with increased temperatures, the clear strip expands at a lesser rate than the rail. That could result in an adhesive shear failure. The black rubber strip also has a lower expansion rate than the rail, but the rubber is more flexible and seems to keep up with the rail.
I have 12 Festool rails and every one that came with the clear splinter guard has spit the bit.