Hi Paul & Mehtaz. Thanks.
I hope the developers will raise attention. It is not permissible to take steps back, it is not permissible in order not to be backward compatibility.
In general, of course frontend interface in SPPB 4 is much better and more convenient. I prefer frontend interface in my work. But the backend interface is always a spare plan. On my test site, various third-party extensions are installed, since I believe that it is precisely such a test environment. No one will use SPPB in pure ecosteum. And the frontend interface built on JavaScript can always cause problems. As it is in SPPB 3 with Engine.js errors.
I saw a comment of one of the developers about returning to the backend interface, they need to make everything from scratch. I do not know what team should do in this case. But world history shows that many promising projects were doomed at the collapse, if they were not redone from scratch.
One example is the fantastic Adobe Muse failed, only by the fact that the developers were not fairly flexible and prudent. That got a project in a dead end.