This counter tracks how many receive-side VBUS backplane buffer overruns have occurred for this module, frames arriving from the backplane that the module had to drop because its receive buffer was full. Rising receive discards specifically point to the module itself being unable to keep up with backplane traffic destined to it, which an admin would distinguish from Tx discards, an outbound bottleneck, when diagnosing where packet loss is actually occurring. If a controller module shows increasing chasModuleVbusRxDiscards during peak hours, it suggests that card's own processing or buffering, not the sending modules, is the bottleneck.