escape sequence in command line prompt

While troubleshooting a problem with rancid running multiple commands on
a VyOS system I noticed that VyOS prefixes the command line prompt with
what appears to be an escape sequence: 1b 5d 30 3b

Anybody know what the purpose of the escape sequence is? It is not sent
during configuration mode and was confusing vlogin’s detection of the
command line prompt.

Those are vt100/ansi terminal escape sequences. See if you can pass an empty string for the TERM environment variable.

TERM="" ssh vyos@your.router