1. Check to make sure you are not exceed output rating of the transformer.
2. Check to make sure their are no unintentional grounds or shorts in the wiring or connectors that may be causing overload and/or surges.
3. Missouri doesn't have significant lightning strike density, thus likely not the problem, but adding a tvss/gfci receptacle, or TVSS to the branch circuit supplying the landscape lighting would help against ANY surging events within or from outside the premise wiring.
4. Could simply be a manufacturer's defect or lack of product quality. Upgrade transformer/fixtures to higher quality and performance.
Good Luck...
