Hey @jow, I've tried to remove different parts of model/cbi to find out what's causing the problem, but that didn't seem to help much.
On 19.07.0-rc2 (I don't believe I've had the same problem on rc1) I get the following error:
#### SyntaxError Failed to set the 'innerHTML' property on 'Element': The provided markup is invalid XML, and therefore cannot be inserted into an XML document.
I first thought it had something to do with buttons or js, but even if I remove these lines from model/cbi the error is still there. Also, same buttons code works just fine with no errors with my other luci packages.
Again, I've tried removing different pieces of model/cbi code, starting with this and still couldn't figure out what's not XML-compatible.
Could you please have a look when you have a moment?