it looks like you cannot find the value at that exact time.
It could be due to the fact you are using the Exact AfRetrievalMode while the value has some subseconds in the timestamp you cannot see in SMT.
I would better use AtOrAfter retrieval mode (I try to never ever use exact).
In order to see subseconds in SMT, go to View--> Settings --> Time Format --> Select "PI Time Format"--> Select 0000 from the subseconds drop-down.
Now you will be able to see the complete time of the event in SMT.
Hope it helps!
The reason we were having trouble is that we were taking the timestamp from a table which treated it as a string, we then converted string back to timestamp and it lost the ms value. We no longer convert it into string and we can use the correct AFTime value for our update in PI.