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Your guess is as good as any other. The creditor could have reported it to only 1 for some odd reason or a glitch, or the reported information could have simply only been updated by TU and not the other 2 bureaus. I've had accounts where on one bureau it was clean, the other showed a 120 day late and the third it showed a 60 day late. All dramatically different, but the same account.
Likely a glitch. I have a 30D late which I did earn which is listed on TU but not on EX / EQ.
Got lucky for once, not poking the bear or doing anything else will just sit and wait out the clock on that one. If you didn't earn them (look at your payment and balance history on that account) then of course address it, but if you did earn them... well, with how everything is setup having 1 bureau dirty isn't really a penalty at all, and in general TU is less important for the vast majority of consumers so take it as a win.