try this

before

my $raw = "\x06\x30\x30\x30\x0D\x0A";
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select (undef,undef,undef,.5); # sub sec sleep
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hint via https://volkszaehler-users.demo.volkszaehler.narkive.com/yAisjztI/vz-users-wiki#post14

and https://chromium.googlesource.com/apps/libapps/+/HEAD/hterm/doc/ControlSequences.md#C0 saying \x00 is "ignored", but perl will try to send it.

there was a time break between the two echos that may not have existed in your perl