I've honestly never experienced some "hip popping" while passively stretching middle split (and I am tight). I've never heard it mentionned by other gymnasts or coaches either, which does not mean it does not exist.
I do, however, sometimes feel some clicking/popping in my hip while doing active flexibility, especially when I'm not warmed up enough. I've no idea if it's normal or not to be honest, it's one of those things I just ignore since it's not painful at all. I probably shouldn't though.
I would definitely ask a doctor or a physio (not familiar with the US terminology), especialy if it is painful.
Maybe also slow down on the stretching ? Or at least make sure you are doing it right and did not pick up a bad habit while on quarantine ?
