As someone who does not subscribe to WomensStuff, so I only have general advice for you:

• If you or your instance (still forget the specifics) is opted into Lemmy Federate, then the bot drops a subscription when a real user subscribes. If that real user unsubscribes, I'm not sure the bot picks it back up.
• People deleting their accounts or getting banned from an instance, perhaps? Not sure if banning from an instance drops all the user's subscriptions there.
• Fatigue or dislike with the posts there.
• Maybe just plain old federation issues? I know I have a community where my subscription is still pending, because the instance has massive federation issues.

It happens. I wouldn't worry too much about it unless it drops a good fraction and stays down.