Round-tript time limitation 20 min

Hi All,

I am using LR 12.01

I have a very long script (97 transactions).

I have noticed very strange behavior of my LR...

With the Think-time (in the Run-Time setting) set to 15 sec (max) the overal Round-trip is less than 20 min and the script passed successfully.

But if the round-trip time exceed 20 min, my script starts to fail at check-points in the transactions which fall on 20th minute.

So, my QUESTION:

Is there known limitation for round-trip for LR12.01?

Any help and assistance appreciated!

Thank you,

-Vadim