Bots are not nearly as widespread on Lemmy as they are on reddit. You’re letting your frustration with a slow growing community turn into “old man yells at cloud.”
The main use of bots is for federating. They join communities but don’t interact with posts at all. Even that requires an instance admin to set up so it’s not like there are thousands of them or something. Bedsides that the rest of them are mostly news and information shares.
Lemmy is much smaller than reddit and has more barriers to entry and community growth. Expect it to take months to get a community off the ground.
I can’t say for certain but the fediverse is prone to behave unpredictability at times. You’re probably better off thinking about Lemmy as a collection of websites rather than one central hub like reddit or more traditional sites.
Instances go up and down all the time as well. Sometimes when a site goes down for maintenance (and probably other things like sync issues) the subscriber numbers will fluctuate because a bunch of them are on a site that “doesn’t exist” for a short time while it’s being worked on.
Everything you do on Lemmy takes longer than what you’re probably used to on a more traditional website too. Your posts to your local instance should be instantaneous but sometimes it can take minutes, hours, or even days for those actions to fully federate to other places. This is true of posts, replies, votes, and subscriptions.
There is also defederation which can cause the behavior you described. You are on one of the largest instances on Lemmy and some people have soured on it and its users. It’s entirely possible some of your subscribers were on an instance that defedderated with lemmy.world or something.
TLDR: You are likely overthinking the impact of bots and putting too much importance on subscription numbers. Make sure the community you care about can actually reach the people who might be interested and hope for the best.
Only slightly related but maybe you’d be interested -
I put together a help post for new Lemmy users on my instance describing how to find and join new places on Lemmy. Maybe these resources will help you understand more about how Lemmy works and how you can get your community off the ground.
https://walledgarden.xyz/post/1600683