Well msm8996 is supposed to have the big core clocked at up to 2.16Ghz (Turbo), and AFAIK only the MSM8996 Lite version is limited to 1.8Ghz.
But here not sure if this frequency really refers to the CPU cores (I don’t have bootloader source code), maybe it’s just the memory frequency (LPDDR4 SDRAM at 1866 MHz clock rate).
on my side, I also get 1.8Ghz:
B - 568001 - 8996 v3.x detected, Max frequency = 1.8 GHz
Whereas my SoC (APQ8096 3.1.3 on the PCB) is clearly identified supporting Kryo Gold 2.15
GHz in the Qualcomm® SnapdragonTM 820E Processor device specification  (4.3).