Adding more dependencies to a task, and now I don't have any start/end date info, just duration

I had a task that hadn't started yet, that was reliant on another task.

I had start/end dates, a duration, and the dependency listed in it.

Now I need to add 2 additional dependencies and see how it impacted timing, but it deleted the start/end dates when I added these extra dependencies in. If I try to put today's date in as a start, it just tells me that if I want to use that start date, I need to delete the dependencies. Huh? I've tried all kinds of dates to no avail, same response.

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