Tom, sorry for the trouble you're having. I can commiserate as I and many others are having the same problem you're encountering. Something went amiss with respect to the core "Like" (fka bookmark) plugin and the Known Reactions plugin somewhere after v0.9.2. It's this that is causing issues with Likes and Reposts. It's a Known issue (pardon the pun) which is documented here: https://github.com/idno/Known/issues/1753
Feel free to add your experience to the issue (which will also bring it back to everyone's attention again) and hopefully someone will figure out what is going on in the march to release v1.0 of Known. I suspect that the functionality in saving things to the database works, but that the output display is having issues as is the sending of webmentions so that they show up on other's sites.