System generated Created (Date) column keeps changing itself to regular Date column.

I have a column that I'm setting to the type of Auto-Number/System that I'm setting to Created (Date). Some time later, it changes itself back to a regular Date column. I've re-set it numerous times and it keeps happening. Each time, I save and re-fresh and it stays for awhile. I've moved around and added and deleted columns and saved in-between each change and exited and re-opened and I can't seem to make it change back by any certain thing. It just randomly will have reverted back to a regular Date column some time later and I have to re-set it.

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