while (<LOG>) consumes the line from the buffer. So, you find the starting line in the first while-loop, then continue from the next line in the second while loop.

Is there a reason you have the while-loops separated? Why not combine them and instead of breaking out when you find the first line, set a flag that says "I should be handling these lines" once you find the first good line. So, instead of "last when found", do "next unless found or this line is ok".