This reports how many modules configured on this phase are not currently detected on the bus at all, the phase-level count of modules failing the basic presence check in tsiModuleSeen, and functionally the complement of tsiPhaseNbModSeen against tsiPhaseNbModConfigured. It is a distinct category from tsiPhaseNbModKO, since a module that's simply not seen gives no fault code or diagnostic detail at all, pointing troubleshooting toward comms or cabling issues rather than an internal module fault that would otherwise report through tsiModuleStatus. An admin seeing this count rise on a phase, with no corresponding rise in tsiPhaseNbModKO, would suspect a bus wiring or connector problem affecting communication to that specific module rather than a power-related failure.