Hi,
Thanks. I note that memory_limit is only 128Mb, which is very low for a modern PHP site (from our stats, 90%+ will have 256Mb or more).
I'd suggest raising the memory limit, using the guidance in this article: http://updraftplus.com/faqs/deal-fatal-error-allowed-memory-size-errors/ (or raise the default in your php.ini). Then check the UD log file on a fresh backup to confirm that it's taken effect (its logged near the top).
David