Can baclofen lead to my leg buckling?

Yes: Assuming you are using Baclofen for spasticity due to e.g. Stroke or ms: a weak and hypertonic (spastic) leg may need some spasticity to keep the leg extended (straight) using antigravity muscles (hip and knee extensors, ankle plantarflexors). Reduction of tone by too high a dose of Baclofen may reduce the degree of spasticity below what is needed to keep the leg extended.