Problem resolved. The ASRock Rack X470 motherboard requires manually forcing a split between two of the PCIe slots when using two x8 PCIe devices under specific conditions that my setup required. I updated the setting in the BIOS and both HBAs are now seen and all data and cache drives are found and array started error free.
I may replace the two 8 channel SAS/SATA HBAs with a single 16 channel device to make things a bit cleaner.
