Issue now appears resolved with upgrade from 3.1.0 to 3.1.1
I have found the problem: it’s all appears to be the fault of WooCommerce.
I have started another thread specifically to address this: https://ww.wp.xz.cn/support/topic/when-woocommerce-is-activated-all-pendingspamdel-comments-appear-in-rss-feed/
