I don’t know what state the JavaScript Helper Libraries are in for OH 3. I haven’t been using them. I know that there is a PR to fix the Python Helper Libraries to work with OH 3 but I do not think the JavaScript ones have been fixed. utils.js seems to do a lot of importing so I would not be surprised if the problem is with one of those imports.
But I would have expected there to be errors in the logs. So I can’t offer any advice beyond adding some logging to the library code itself to see if you can tell where it’s failing.
GitHub - openhab-scripters/openhab-helper-libraries: Scripts and modules for use with openHAB is the official repo for the libraries.
Yes, you can use them in the UI rules. Not all of the libraries will be relevant in UI rules since you will not be dealing with triggers and creation of rules and such.
And contributions are welcome. If you see something you can write please jump in and open an Issue and PR and start contributing. The barrier to contributions is as low as we can make it. However, the Helper Libraries are not (yet?) a part of the openHAB project. Consequently any documentation for them needs to be made in the Helper Library repo, not the main OH docs.
Unfortunately I’m not using the Helper Libraries because until they are released as an add-on most non-technical users won’t be able to get over the hurdle of getting them installed. So I’m focusing my efforts on learning how to do everything without the Helper Libraries.