I've confirmed the partial read with some local modifications, and the failures are always split between time stamp and value:

Warning -- Failed to parse typeperf output: '"10/02/2019 17:42:26.229"'
0.0
Warning -- Missing first field: ,"0.000000"
0.0

Adding multiple variables to the typeperf command can vary the split position, but I've only seen it at a variable boundary (starting with the comma).  So I'm guessing with the current implementation the above is probably the only point where the I/Os can be interleaved.

Also, CRLF seems to only appear at the start of each read, never at the end.  You can see that behavior interactively too where the cursor waits at the end of the line between samples.  So changes to wait for a complete line to be read would also delay load values by one sample interval.

So I'm thinking just reverting to silently ignoring this case is probably simplest.