When did you post the post with the best reach? Are the hashtags you used there all related to the newer posts you tried using them with?
Meme/repost pages have a harder time now, Instagram stated in late November early December that they prefer original content over reposted content and that the algorithm will reflect that in the future.
How many hashtags are you using? Are they all related and the right sizes for your account? Do you have different sets for different topics?
How did you gain your followers? Are you doing follow for follow? If yes, people who followed you back might not be interested in your content and just scroll by your posts until they’re not even show up in their feed.
Followers who follow more than 1,500 people most likely never see your content anyway if they’re not spending *hours* at a time scrolling their feed. The fairly new misleading “You’re all caught up!” message makes it worse.
Not sure if you’re already interacting with your existing audience, but that’s what I’d recommend as a first step. If you’re not already writing engaging captions with a clear call to action and preferably an easy to answer question that’s related to your content, start doing this now.
Reply to every comment, even to those annoying automated “Nice pic ?” or “???” comments. Thank them and wish them a nice day. If you get a real comment, pin it! You can pin up to three comments per post, people get a notification that their comment got pinned and they feel like their effort was appreciated. They will most likely comment again.
Write meaningful comments on your followers’ and followings’ posts. That will not only encourage them to return the favour, but their audience will notice you as well.
What does any of this have to do with hashtags?
If even your own followers (the people who signed up to see your posts) don’t interact with your content, Instagram won’t show it to more people outside your existing audience.
Get decent enough engagement from your existing audience and your hashtag reach will improve (if your hashtags are relevant).