Just as an info (I'm sure that you are anyway working on that with high priority), this problem currently delays our system rollout at one of our biggest customers
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it seems that the performance problem is connected with the inactive setting. In the problematic example all tasks have been set to inactive. When we change to have them to inactive:false it is fast.
after some tests we found out that the faster behaviour was just when we added something to the end or deleted something from the end of the list, sorry for the confusion
@pincherhgz Hi, we've recently fixed one very similar performance problem https://github.com/bryntum/support/issues/6262, perhaps it has the same root cause as this one. Can you please verify? (Will need to use nightly build, the fix is not released yet)
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@pincherhgz Hi, sorry for delay, this issue has been resolved and merged. You can verify it in the next release or in the tomorrow nightly build.
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