I'd recommend you upgrade to the latest Q firmware (official download link: https://dlcdnets.asus.com/pub/ASUS/ZenFone/ZS620KL/UL-Z01R-WW-126.96.36.199-user.zip)Thanks.
I tried in 2 different pcs with different os (W7 and W10) but still return the same error.
Ps: i saw a strange thing:
In points 1,2,3 I am with the bootloader 188.8.131.52 but when I reboot as in point 4 the bootloader has changed to 184.108.40.206.
Or just flash fbrom: https://broad-bread-4cee.reignz.workers.dev/[up_vnROM.net]_WW__ZS620KL_220.127.116.11_MR13_20200520_release-user.raw.zip