1.Did you try using the wpa_supplicant command for changing the bandwifths.
2. We do provide regular updates to the CLM BLOB(regulatory binary that goes along with the firmware) for every release of the fmac.
It looks like the firmware update zip doesn't include brcmfmac43430a0-sdio.bin or brcmfmac43430a0-sdio.clm_blob, would you be able to provide said files with the latest driver package (v4.14.77-2019_0503) ? This relates to the chip CYW4343SKUBG.
Thanks in advance,