Please help me understand why this unit test fails unpredictably

I just ran pytest twice, with contradicting results. The first time, I got a failure in TestData.test_sample_posterior_predictive_after_set_data_with_coords:

E       AssertionError: 
E       Not equal to tolerance rtol=1e-07, atol=0.1
E       Mismatched elements: 1 / 2 (50%)
E       Max absolute difference: 0.12025266
E       Max relative difference: 0.02045201
E        x: array([5, 6])
E        y: array([4.920059, 5.879747])

Then I reran the tests again (without changing anything in between). This time, the same test is passing. Is this expected behaviour?