Thanks @borpin for highlighting the MQTT issue.
We needed to push forward the merge to stable, so that Glyn could finish compiling the RPi3 B+ SD card image with stock running low on the old variant. I was mostly sure that there were no breaking changes but with a lot of other things going on in parallel over the last week was not able to give it my full attention.
The changes have been in master for testing for months (our pre-release stage) and apart from ongoing work on the new interfaces which are still in beta and subject to ongoing development, I thought we had all key bases covered.
As ever there have been a couple of missed issues, in particular arising from not adding the code to automatically clear browser cache on the inputs interface and the need for upgrade notes for publish to MQTT.
I will put together a release post on the forum today.