Remedying the immediate issue is fairly straight-forward - either repair or replace. The more important issue is the design of commercial baluster systems - these tend to routinely put vulnerable end grain and fresh water together - a recipe for both paint failure and wood rot. You may want to consider either an aggressive sealing and painting routine on painted work or looking at whether a design change can help.
19 years ago, I replaced a standard porch railing system with one designed to shed fresh water. The porch is a wrap-around on the north and west sides of the house, running about 70 feet of railing between wood columns. The original builder's railing had rotted out after about 7 years of service, with the finger-joined pine and lower railings under the balusters disintegrating. The replacement used dual upper and lower rails that captured the 1-1/8" square balusters, but let water flow through to drain away. The rail sections - up to 14 feet long - were mounted on blocks captured between the rails. Despite using big box 2x spruce and pine without any treatment, the design has prevented any rot with what has been an 8 year pull and paint cycle. As a bonus, the block system of mounting makes for a tool-less removal, so painting can be done off the porch with an airless system.