Context: I am a fairly new intern, with an assigned mentor who is expected to be my first line of help when/if I need it. Our most frequent communication is via an internal IM system, which is nice because we can quickly message each other and send code snippets/links back and forth.
My one issue, however, is that sometimes I send a question and get no response, or we are having what seems to be a lively chat and then he disappears. Of course, I understand that perhaps someone has walked into his office/he is distracted by other work, but if I go more than an hour or so without response I am antsy because I may need this answer to move forward in my tasks (I don't want to be the do-nothing employee on their phone all day).
What are some good ways to follow up an unanswered IM that will not be construed as nagging/impatient/escalating? I tagged this software dev as it might help give context for the culture: I've debating just messaging him "still need this" or even "bump", but am not sure if it would seem disrespectful. Stopping by his office in person occasionally works, but is sometimes met with "sorry, I'm fixing a prod issue, I'll get to you later" (which I find embarrassing). I think email would be entirely overkill for what usually amounts to a small issue. Advice?