Yeah, in the last year I've barely got 100 new subs but most recently I gained a whole bunch of new ones because I upped my networking. Not saying you personally but one reason why people have dry patches does depend on their networking habits. You can be consistent on making videos and be a good content creator but what some forget is you need to be a good viewer too. I'm now checking my sub box daily and leaving comments and likes with those who i enjoy...mostly smaller youtubers as they appreciate my interactions far more than the big youtubers who would hardly notice. Doing this brings youtubers to my page and I get comments and likes which has helped me grow.
Also looking for new small youtubers to watch is something I love, again finding them, saying hi, watching and interacting with their new videos when they upload them. Doing this has brought me new peeps to my channel and they seem to return consistently when i upload something new which I cherish but I'm always a real person when leaving comments as I don't do the whole "you're channel is amazing and I've subbed, come and sub to mine please!" That is the worst thing you can do.
Another thing I do is when I'm waiting for my new video to upload I reply to comments on my videos if i haven't already done so and go to their channels to see if they have uploaded anything new which may have not appeared in my sub box and leave comments. Doing this helps me build a relationship with other youtubers and helps me have consistent likes, comments and new subs coming in. I do get the occasional dislike but they are also good for your videos despite most people thinking they are bad. I'm sorry for waffling on but I hope this helps.
talk to other YouTuber's who are on the same level as you and do some collab's 
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