I’m delighted to report that I think I found the problem. My specific access to WordPress – via the WordPress.com site is via Firefox – completely up to date etc etc. I have two plugins running – Ghostery and UBlock Origin. Initial testing seemed to suggest neither of these applications were causing the problems around saving that I’ve been having. Indeed, when trying to use Chrome to edit my posts here at the office, I have had the same issues.
I have since reviewed our corporate firewall rules, routing and filtering to no avail (although there was some weird, unrelated stuff going on that I fixed causing much happiness in the office). I tested access to Gutenberg at home and it was all good, so why not here at work?
Long story short – it was the Ghostery plugin! Oddly it appears to behave differently at home to work – no impact on my WordPress activities at home, but stuffs things here at work. I am writing this right now at work, with Ghostery disabled and Gutenberg is doing the job! It’s saving properly and I’m quietly thrilled by it! Now I can get on with the business of learning a whole new editor! Dave from WordPress (Automattic) has been working with me to fix this and I appreciate the assistance. Let’s get to it!