in the "humanReadable" segment of the backtrace dump,
and in the case that it was given a sink (not writing to LOGV2),
we emit frames like this, but there's no terminating newline.

*sink << fmt::format("\n Frame: {}", tojson(frame, ExtendedRelaxedV2_0_0));

Need a newline. This section of the output is specified to emit lines.
Without a newline, it's not a line. Trivial fix.