If the field corId is unique to each transaction, then you can use stats instead.
For example, you could run
<your search> | stats values(*) as * by corId
You would get a table of each corId and the events that have that corId field. There are huge benefits to not using the transaction command. The search will run faster, and be more accurate (over large event sets transaction will throw out events to save memory)
On another note, I would check your NTP configuration. 4 secondstime delay is a big difference!
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