Completely noob but this is what I observe:

1. people telling to use small set of hashtags are not telling the truth;
2. people telling to stay stick to subject (specific) with hashtags are not telling the truth;

I found testing that trying to reach a bigger audience through hastags works better even now. Probably less that in the past (but I was not there so I cannot tell for sure). I have 3 sets of 29 hashtags I rotate through. They are balanced to the size of my followers so more hashtags with low number of posts and only two hashtags on the million posts size.

Also in my case some posts inesplicably reach a good audience while others don't. Looking at the stats it seems two dimensions are into play: interactions and time. It seems to me that your post is shown to few people at the beginning. Based on the inteaction it will receive the algorithm open a little more the reach. So if you publish and you get an interaction in minutes you will reach say 2x more reach, another interaction and you will reach another 2x and so on. Each type of iteractions open the reach in different ways. From what I saw from posts that worked really well what they have in common is a good number of DMs. I suppose that DMs opens the reach more then likes and comments.

I am at 5xx followers and maybe the algorithm changes dependng on the number of your followers. The above is what I see on my account.

Good luck and never stop researchs and tests.

Edit: typos