Can't save output of particular command in particular environment (cron)

My crontab is not producing logs for a particular command I’m using to monitor my network; other commands work fine.

* * * * *    /usr/bin/COMMAND opt1 opt2 >> /home/pi/LOG.log 2>&1

The log file is created, but the output of the command does not log. The command and logging works fine when run in it in the terminal. I’ve tried copying the cron environment and running the command manually:

With crontab -e, I added:

* * * * * env > ~/cronenv

Then I run:

env - `cat ~/cronenv` /bin/sh
/usr/bin/COMMAND opt1 opt2

The COMMAND outputs as expected, but as soon as I try to log the output, I get empty logs:

/usr/bin/COMMAND opt1 opt2 > /home/pi/LOG.log 2>&1
/usr/bin/COMMAND opt1 opt2 | tee /home/pi/LOG.log 2>&1

Switching my shell in crontab -e to SHELL=/bin/bash also has no effect.

Not sure if it’s relevant, but the command I’m struggling with takes several seconds to run, outputs in color with somewhat fancy formatting, unicode characters, etc. when I run it in the terminal, but it still logs fine. When I run it from the cronenv I created, it does not display in color, but displays in much the same way it does when I save it to a log from terminal.

EDIT:

This is working in the ~/cronenv environment I made, but the log is created but empty when run through cron (as before):

/usr/bin/unbuffer /usr/bin/COMMAND opt1 opt2 > /home/pi/LOG.log 2>&1