How to run a remote command in PuTTY after login & keep the shell running?

What the -m does is, that it makes PuTTY instruct the SSH server to start that command(s) INSTEAD of a shell. So once your command finishes, so does the session.

If you want to run the shell after the cd command, you need to add it explicitly to your cmd.txt, like:

cd /my/path ; /bin/bash

Also the -m implies "nopty"/non-interactive mode. To use an interactive shell you need to override that using the -t switch.

putty.exe -ssh example.com -m "c:\path\cmd.txt" -t

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Alternatively use KiTTY with its -cmd switch, that does what you want (and does not need a temporary file).