Create and use bat files that set and use environment variables, but environment variables are null

@echo off
setlocal

set "inputIpList=%~dp0IP_list.txt"
cd  "Program Files7-Zip"

for /f %%a in (%inputIpList%) do (
    echo "Processing entry: %%a"
    set a1=%%a

    echo %a1%
    timeout /t 5
    "Program Files7-Zip7z.exe" x -so "%~dp0monthly%a1%var-log-files.tgz" | 7z.exe x -aoa -si -ttar -o%~dp0monthly%a1%
    

    for /l %%b in (9 -1 0) do (
    echo %%b
        set "b1=%%b"
        echo "Extracting messages.%%b.gz"

    "Program Files7-Zip7z.exe" x -so %~dp0monthly%a1%messages.%b1%.gz >> %~dp0monthly%a1%messages-merged.txt
    )
    type %~dp0monthly%a1%varlogmessages >> %~dp0%a1%messages-merged.txt
)

endlocal
pause

“%~dp0monthly%a1%var-log-files.tgz” is output as

".monthly\var-log-files.tgz"

Why is this happening?

Is it the way to run the next line before the previous command line is completed?

I’ve added a timeout command

set a1=%%a is change

set “a1=%%a”