Double batch fermentation question

[Beardown]

This is our 1st crack at double batching. We are double batching 2 3bbl batches into a 6bbl fermenter 24 hours apart. We brewed the 1st batch and oxygenated as usual and pitched enough k97 dry yeast for a normal 3bbl batch. We came in the following day (today) expecting to see some kind of fermentation activity but there was none and no gravity change. Our normal 3bbl batches into 3 bbl ferms usually have noticeable fermentation activity by the next day with this yeast. Does this have something to do with the 6bbl ferm have much more headspace? I know it's only 24 hours after pitch, it just caught us off guard a bit.

[dick murton]

Is the temperature probe above the wort level? If so it may be giving a falsely high reading and causing the cooling to come on, overchilling the wort and stalling the fermentation.