I nearly lost my LVM thin pool on my laptop recently due to the metadata nearly filling up (99.4%). I first noticed this when trying to install something and the root filesystem was read only. Rebooting the machine re-mounted the root partition as RW. Trying to get this pool into a healthy shape gave me all sorts of transaction id and meta errors so hopefully this post will assist someone.
My LVM Layout
I use LVM on my Fedora 27 system along with encryption; it is probably useful to share the layout so the rest of the blog makes sense.
Using the LVS command: