It sounds all kinds of broken, and will probably be easier to start over with a clean install. I spend quite a bit of time persuading clients to not use WordPress (or any other CMS), because the baked-in limitations and problems far outweigh any supposed benefits. Yes it enables 'anyone' to get a website up and running, and start bolting on all kinds of crazy 'features' wily-nily. Therein lie the problems, and they are myriad and frequently unsolvable. For those who insist on forging ahead, I advise them to use the standard configuration without any customizations.

That's just about what I'm aiming at. It looks like it's been constructed without really thinking what the "customers" would expect/want, rather than being heavily customised, so I'm hopeful I can get it better if not perfect.

Some of the things will be easily fixable, such as the Recaptcha problem because that's a classic case of the admin not quite knowing what needed to be put in place before installing it. Others such as the vanishing posts may have been fixed in later releases as the first thing I noticed was how out of date a lot of it is. I'll just have to see how it goes.