Sooner or later, they start to fall. We're talking about reach - that is, the total number of people who viewed your post.
Competition, algorithm updates, a general decline in social media activity (for example, on weekends) - when you look at the statistics of a group or account, you immediately notice the spikes due to this.
But in general, fluctuations are possible and nothing to worry about. Moreover, posts can differ from each other in the number of comments and likes by about 30%. And this only means that your account or group is "live", without fake results.
But there are situations when the reach suddenly drops seriously and for a long time. And there can be different reasons for this failure.
Non-targeted subscribers
Random people - "Friends" who are not interested in you, subscribers "for the sake of quantity", commercial accounts that are never read at all, abandoned pages. The algorithms see it this way: people subscribed, which means they showed interest. And now they don't show interest (they don't like, repost, save, or comment), which means it's your content. If you're making "nothing", we won't show you to others.
The more such subscribers there are, the more noticeable the drop in coverage. Keep an eye on your subscribers and periodically clean the list of the most suspicious ones.
The same hashtags
Hashtag sheets no longer work for promotion. The social media algorithm can mistake a large number of tags for spam and remove you from the feed.

Cheating
Purchased comments and likes hurt the reach. Bots do not show any activity, and this will affect the statistics. They can also block you completely.
Useless contests and Givas
After them, going after subscribers is like looting a store. A lot of fuss, a lot of activity and movement, but in the end, you only suffer losses. You don't have your target audience in the givens, but only freeloaders who participate in all the draws indiscriminately. They fulfilled the condition of the promotion, subscribed, liked and forgot about you.
Not interested in the content
The objective reason is that your subscribers don't need it. Boring texts, the same topics, unimpressive design - all this does not evoke a response. Look at your content plan and analyze your target audience again.

Complaints about your account
Violated copyright, posted someone else's text or photos, links to a brand without permission. Offensive content, controversial texts, aggressive statements. All these are reasons to click the "report account" button, and the reach goes down.
Shadow ban
It cannot be detected without monitoring the coverage. The situation when the reach drops unexpectedly and very strongly. Your posts are removed from the feed, the system does not find them by hashtag. You are confused because you did not receive a warning or a ban. You can get under this implicit blocking for using the same hashtags in more than 3 posts in a row, using more than 30 hashtags, complaints from other users, changing posts too often.