Only a couple of possibilities here.
1 - Different scoring models are being used. You already said this isn't the case, though.
2 - The scores may be using the same scoring model, but are using data from different bureaus.
3 - The scores were generated at a different time.
I'd go with #3 here. While a source may give a score today, it could have been generated at an earlier time. Take Discover for example. They typically update my score on the 3rd or 4th of the month. That score however is usually generated on about the 27th of the previous month, so roughly a week earlier. If something significant changes in that week and I pull my scores on the 4th (the day I see my new score from Discover) from CCT, my CCT score may be quite different. My mortgage company also always seems about a month behind, even though it dates the score for the current month it always to me looks like the score is from the previous month as I've had major scoring changes happen and the FICO 08 score I get from them always takes an extra month to change.
