What's the difference between 行为 and 现象? 从（软件运行的）现象上来看，这个问题不影响软件的正常使用。

According to the dictionary, 现象 is phenomenon. I think it should be behavior, but behavior means 行为.
Besides meaning 'a phenomenon', a more literal understanding of 現象 is 'the appearance of things'*. By character, 現 means 'to appear; to reveal'; 象 means 'resemblance; appearance'. May think of that as 表現之象.
This sentence may mean something like this:
'From the way the software runs, it appears that this problem does not affect the normal functioning of the software.'
In this context, 現象 is akin to 表徵, 表面.
行為 as a substitute of 現象 is grammatically plausible. But their meanings differ slightly; while 行為 is a neutral phrasing, 現象 seems to be a more conservative way of assessing the effect of the problem on the software - the speaker's judgement is only based on how the software appears to them, not necessarily how the software actually is under the influence of the problem.
* Reference: 譯典通英漢雙向字典