The first time someone on an instance enters the name of a community, is when the instance goes and looks for it. Until then, that particular community is not federated to the local instance, and it is as if it does not exist.
Searching for a community in Jerboa, does not seem trigger this establishing of a connection.
I wonder how many communities on smaller (or even larger) instances there are that people just don't know about because they didn't know to look for them.
I'm on latte.isnot.coffee and I just searched both !jerboa@lemmy.ml and https://lemmy.ml/c/jerboa and didn't get results for either. Neither has a message saying that there are no search results, but neither shows any results either.
I can sometimes get them to populate if I do it twice or change it from Communities to All in the search filters. Other times, it just takes an extra 5-10 seconds after returning no results.