Page titles/date stamp automatically overwriting new stuff

Hi – I’m new to this forum so apologies if anything wrong here. My wordpress installation (at https://www.emdreastassoceastanglia.org.uk) has suddenly started generating automatic page and post titles, and a standard date stamp, from an earlier post, and overwriting on save anything new I try to write. I’ve cleared my browser caches, cleared wordpress cache, and it keeps happening. Any ideas very gratefully received.

thanks

Mark Brayne