What breadboard are you using?
Quality really does matter (contacts wear out & make intermittent connections).
There's a few threads that cover this, but IIRC, look for Wisher on the budget side (sold under multiple brands, such as Elenco, Radio Shack, and others; not sure if they make them for RS or not). Past that, Global Specialties (preferably not the E <economy> line) or 3M. These are more expensive, but I've seen ~30y/o breadboards from them that still work as they're supposed to.
Maybe check eBay for NOS (there was a seller in the US that had misc. 3M NOS). BTW, get one with a metal back plate if you can.