This field is part of the PCIeFatalStats table's tally of surprise-link-down errors on this compute node's PCIe fabric — this specific fault fires when a PCIe link drops to the Down state without going through the normal, orderly link-training/removal sequence. This is the historical high-water mark: the highest count of this error type ever recorded in a single 15-minute window within the retention history UCS Manager keeps for this compute node's PCIe fatal-error stats, so a quiet current reading doesn't hide an earlier 15-minute burst. For example, if this counter shows 5 while the live 15Min bucket currently reads 0, it means five such errors (e.g. a mezzanine card or riser losing electrical contact (a loose card or failed slot) instead of an operator-initiated, orderly card removal) occurred together at some point in an earlier 15-minute window, even though none are happening right now.