I am running jmeter script on azure cloud platform and executing soak test. Mentioned total duration of 28 800 sec (8 hours) in jmeter script. But, execution getting completed automatically after 3 hours, (test not able to last long for 8 hours). I re run the test 2nd time also it gets finished in 3 hours only.
Are you sure the problem is with JMeter? I'm mainly asking because when I look at Azure Load Testing Service limits I can see the default limit of the test duration set to 3 hours:
If you already contacted Azure Support to increase the test duration and test still ends prematurely - take a look at jmeter.log file, it normally contains the reason for the thread/test shutdown (you might want to increase JMeter logging verbosity as well)