Yep, I've had exactly this problem on Instagram. As far as I can tell you can only search for one hashtag at a time, which is why I got into the habit, as everyone else there seems to, of tagging everything with every combination of words you can think of. So to take an example I've posted there, instead of just #cosplay #spidey #milesmorales (which I'd normally think would be sufficient) I end up also adding #milesmoralescosplay, #spideycosplay, #milesmoralesspidermancosplay, etc, etc, just so people can actually find it (the more general hashtags just have far too many results to be worthwhile on their own). It's exhausting!