Hi ,
We have had a couple of bugs reported regarding the undo function not working when a specific action has occurred like dragging a series of buttons in a Widget Blueprint, for instance. However, we have not had numerous reports where this is happening in general. Please take note of what you are doing the next time this occurs and post steps we can follow to reproduce the issue on our end. You can add those steps to this post and we will continue to investigate.
Thanks,