What are factors that can change the results in an experiment?
The wrong phase of the moon; God; you had a late night last night; your current partner is a fruit loop; the lab is
For a third party we simply don't know. The experiment was performed a first time and gave certain results; the experiment was performed a second time and gave inconsistent results. Only you can assess the change in conditions; the change between what you did the first time, and what you did the second time.
This is the reason why scientists insist that experiments be adequately described. Now I was being facetious in the opening paragraph, but at least some of the reasons are valid. And only you can assess the difference in conditions.