[Moto X4 ROMs, Kernels, Recoveries, & Other Develop] unfnknblvbl:
I've tried with three different USB cables, on three different USB ports, in both cmd and powershell (not that this would make any difference)

getvar all gives me:

(bootloader) kernel: uefi
(bootloader) version-bootloader: MBM-3.0-uefi-641a15b-180530
(bootloader) product: payton
(bootloader) board: payton
(bootloader) secure: yes
(bootloader) hwrev: P4
(bootloader) radio: APAC
(bootloader) storage-type: eMMC
(bootloader) emmc: 64GB SAMSUNG DH6DMB RV=08 PV=05 FV=0000000000000005
(bootloader) ufs: N/A
(bootloader) ram: 4GB SAMSUNG LP4x DIE=16Gb M5=01 M6=06 M7=10 M8=12
(bootloader) cpu: SDM630 1.0 (0)
(bootloader) serialno: lolnope
(bootloader) cid: 0x0032
(bootloader) channelid: 0x51
(bootloader) uid: 0FB5AED1
(bootloader) securestate: flashing_unlocked
(bootloader) verity-state: logging (0)
(bootloader) iswarrantyvoid: yes
(bootloader) max-download-size: 536870912
(bootloader) reason: Reboot mode set to fastboot
(bootloader) imei: hahanope
(bootloader) meid:
(bootloader) date: 05-18-2018
(bootloader) sku: XT1900-2
(bootloader) carrier_sku:
(bootloader) battid: SNN5995A
(bootloader) battery-voltage: 4213
(bootloader) iccid:
(bootloader) cust_md5:
(bootloader) max-sparse-size: 268435456
(bootloader) ro.build.fingerprint[0]: motorola/payton/payton:8.0.0/OPWS2
(bootloader) ro.build.fingerprint[1]: 7.57-40-17/23:user/release-keys
(bootloader) poweroffalarm: 0
(bootloader) ro.build.version.full[0]: Blur_Version.27.271.23.payton.ret
(bootloader) ro.build.version.full[1]: ail.en.US
(bootloader) ro.build.version.qcom: <not found>
(bootloader) version-baseband: M660_7036.16.01.69R PAYTON_APACDSDS_CUST
(bootloader) kernel.version[0]: Linux version 4.4.78-perf-g8a19f40 (huds
(bootloader) kernel.version[1]: oncm@ilclbld69) (gcc version 4.9.x 20150
(bootloader) kernel.version[2]: 123 (prerelease) (GCC) ) #1 SMP PREEMPT
(bootloader) kernel.version[3]: Wed May 30 14:43:30 CDT 2018
(bootloader) git:abl: MBM-3.0-uefi-641a15b-180530
(bootloader) git:xbl: MBM-3.0-uefi-dfccc3a-180530
(bootloader) git:pmic: MBM-3.0-uefi-dfccc3a-180530
(bootloader) git:rpm: MBM-3.0-uefi-245b046-180530
(bootloader) git:tz: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:hyp: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:devcfg: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:cmnlib: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:cmnlib64: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:keymaster: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:prov: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) git:storsec: MBM-3.0-uefi-eee7f2d-dirty-180530
(bootloader) qe: "qe 0/0"
(bootloader) frp-state: no protection (0)
(bootloader) ro.carrier: retapac
(bootloader) current-slot: _a
(bootloader) running-bl-slot: _a/_a
(bootloader) running-boot-lun: 0
(bootloader) slot-suffixes: _a,_b
(bootloader) slot-count: 2
(bootloader) slot-successful:_a: yes
(bootloader) slot-successful:_b: yes
(bootloader) slot-unbootable:_a: no
(bootloader) slot-unbootable:_b: no
(bootloader) slot-retry-count:_a: 6
(bootloader) slot-retry-count:_b: 6
all: listed above

In the "Bootloader Logs" screen, I get:

cmd: download:019ef000

..on the official twrp image. I even tried renaming it to "boot.img" incase it made any difference.