This is interesting, I'm running into the same issue. As I reached of milestone of 156 tests, all subsequent tests start to fail with the same error. I frankly don't care about it cuz it forces me to run in parallel which makes me believe it's only a time issue. For me, any test that exceeds 1hour and roughly 10mins I get ....
| WARN | Keyword 'Capture Page Screenshot' could not be run on failure: No browser is open |
And then a FAIL on the test.
When I run this test on it's own or in parallel it runs as expected and passes.
I'm on chrome driver version 2.9 on Robot Framework 2.8.3 (Python 2.7.6 on darwin)
Abhilash, I would consider running running your tests in parallel.