Byobu/screen constantly freezes in Putty

You can directly attach to a previously detached byobu/screen session including the window:

byobu -r -p2

will reattach into window 2 (or a named one).

-X can send any command to a byobu/screen session and also works with the -p switch.

byobu -p2 -X stuff "uname -a $(echo -ne '\r')"

This will send a uname -a to the second (third actually) byobu window, the echo at the end sends a carriage return so the commands gets executed.

It could be many things.

Please provide the output of:

echo $TERM
echo $LS_COLORS
typeset -p LS_COLORS
alias ls
tput setaf 1 | od -c
echo "$(tput setaf 1)red$(tput sgr0)"

Expected results:

xterm (optional, see below)
no=00:... (or similar, should not be empty)
declare -x LS_COLORS="no=00:..." (ditto)
alias ls='ls --color=auto' (or similar)
0000000 033   [   3   1   m
0000005
red (in red)

My guess: TERM is set to something unusual, and dircolors doesn't know about it, therefore ls doesn't know what colors to use.

If this is the case, running the above commands inside your byobu/screen session, you would see:

screen (or screen-something)
(nothing)
(nothing)
0000000 033   [   3   1   m
0000005
red (in red)

Confirm that this is the case by running:

dircolors -p | grep "^TERM $TERM$"

I would expect it to print nothing.

The simplest fix, depending on your configuration, would be:

dircolors -p > ~/.dircolors
echo "TERM $TERM" >> ~/.dircolors