The log file used to be the reason. But meanwhile the log file(*) has an automatic limit of 500 lines, so after that it removes a line for every new line added. So that should not be the reason anymore. Still, I recommend to turn of logging if you do not need it, it makes the macro run faster!
(*) The limit is for the in-extension log. The hard-drive log does not have and does not need such a limit.