Grand Central SAMD51 Failing to upload consistently on MAC

The Grand Central fails to upload the program most of the time. Powering off helps, but not always. It seems better with tiny example programs. It is difficult to accomplish anything - sometimes it just won't upload no matter what, other times after 3-6 tries, and other times right away.
It gets to varying percentages.. below is the printout of a failure that is 0 percent:

I've upgraded to the latest UF2, no change, and I've tried different Adafruit SAMD board support versions, no change.

MacOS Big Sur Version 11.1
Arduino IDE 1.8.14 Hourly Build (I have tried all versions of the IDE, originally with the latest release - doesn't seem to matter)
Adafruit Grand Central M4 SAMD51
UF2 Bootloader 13.13
Arduino SAMD Boards. V 1.8.11
Adafruit SAMD Boards V 1.6.6

PORTS {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.PLTBBFIT3150-SerialPort, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.PLTBBFIT3150-SerialPort, } / {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.PLTBBFIT3150-SerialPort, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.PLTBBFIT3150-SerialPort, } => {}
PORTS {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.PLTBBFIT3150-SerialPort, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.PLTBBFIT3150-SerialPort, } / {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.PLTBBFIT3150-SerialPort, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.PLTBBFIT3150-SerialPort, } => {}
PORTS {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.PLTBBFIT3150-SerialPort, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.PLTBBFIT3150-SerialPort, } / {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.PLTBBFIT3150-SerialPort, /dev/cu.usbmodem14101, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.PLTBBFIT3150-SerialPort, /dev/tty.usbmodem14101, } => {/dev/cu.usbmodem14101, /dev/tty.usbmodem14101, }
Found upload port: /dev/cu.usbmodem14101
Library/Arduino15/packages/arduino/tools/bossac/1.8.0-48-gb176eee/bossac -i -d --port=cu.usbmodem14101 -U -i --offset=0x4000 -w -v /var/folders/18/85mvxsh15xvd01nzl1cbhxs40000gn/T/arduino_build_12329/BoyancyEngineTest.ino.bin -R
Set binary mode
version()=v1.1 [Arduino:XYZ] Feb 21 2021 21:10:25
Connected at 921600 baud
readWord(addr=0)=0x2000dfe0
readWord(addr=0xe000ed00)=0x410fc241
readWord(addr=0x4)=0x575
readWord(addr=0x41002018)=0x60060000
write(addr=0x20004000,size=0x34)
writeWord(addr=0x20004030,value=0x80)
writeWord(addr=0x20004020,value=0x20008000)
version()=v1.1 [Arduino:XYZ] Feb 21 2021 21:10:25
readByte(addr=0x804000)=0x39
readByte(addr=0x804001)=0x92
readByte(addr=0x804008)=0xff
readByte(addr=0x804009)=0xff
readByte(addr=0x80400a)=0xff
readByte(addr=0x80400b)=0xff
Device : ATSAMD51x20
Version : v1.1 [Arduino:XYZ] Feb 21 2021 21:10:25
Address : 0x0
Pages : 2048
Page Size : 512 bytes
Total Size : 1024KB
Planes : 1
Lock Regions : 32
Locked : none
Security : false
BOD : false
BOR : true
Write 44536 bytes to flash (87 pages)
0% (0/87 pages)
write(addr=0x20004034,size=0x1000)
SAM-BA operation failed
An error occurred while uploading the sketch