mcumgr hangs during image upload

[dkhayes117]

I have a thingy91 that has been flashed over JLINK which has wiped out the MCUBoot.  I'm attempting to get it back using mcumgr.  I have mcumgr all setup, but when I run

mcumgr --conntype=serial --connstring="/dev/ttyACM4,baud=115200" image upload thingy91_asset_tracker_v2_ltem_2022-06-02_880c82db.bin 

nothing happens after the progress bar appears.  It just stays at zero percent.  I check to make sure I have correct ACM port each time.  I'm running on Ubuntu 20.04.4 LTS.  Any ideas what I'm doing wrong?

When I try to connect to LTE Link Monitor v2.0.1, the ttyACM port shows up and the logs shows Modem port is opened.  If I try to run an AT command, I get a timed out message.

[dkhayes117]

I was able to flash `thingy91_at_client_2022-06-02_880c82db.hex` to the board, but I still can't use LTE Link Monitor.  UART flashes from yellow to red.

13:06:45.310	Modem port is opened
13:06:49.538	Error: 'AT+CFUN=1 ' timed out
13:06:56.718	Error: 'AT+CFUN? ' timed out
13:07:11.476	Modem port is closed
13:07:13.309	Modem port is opened
13:07:17.914	Modem port is closed
13:07:17.953	Modem port is opened
13:07:22.014	Error: 'AT+CFUN=1 ' timed out
13:08:44.003	Modem port is opened
13:08:45.579	Modem port is closed
13:08:45.621	Modem port is opened
13:08:51.448	Error: 'AT+CFUN=1 ' timed out
13:10:27.053	Network search failed: Error: 'AT+COPS=? ' timed out
13:10:28.056	Error: 'CEREG? ' timed out
13:10:29.060	Error: 'CEREG? ' timed out
13:10:30.075	Error: 'CEREG? ' timed out
13:10:31.079	Error: 'AT ' timed out
13:10:32.091	Error: 'CEREG? ' timed out
13:10:33.096	Error: 'AT+CEREG? ' timed out
13:10:34.102	Error: 'AT+CEREG? ' timed out