"loadBranch" does not work correctly if you use Promises way. (Second brunch does not open)
Besides, the callback's don't always work right.
For cases when several requests go one by one, the correct syntax would look rather like this: https://snippet.webix.com/e9ynrq5y
For callback, it should definitely work. However, the promise chain for the second tree also doesn't work as expected. So you are right. I can confirm the issue. Thank you for your report!
And if the time difference between the request is decent, then everything is in order (the first request is completely finished, so the second does not fall into the "unsuccessful queue"):
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