there are multiple layers of potential problems that could be identified in this scenario and explain the cause.
it is possible that this can be a shadowban. by a shadowban, it does not necessarily refer to a "complete lack of visibility" , it can also refer to a huge percentage of drop in traffic, like you are experiencing.
so to summarize i would refer to this as "algorithm cycles" or a "shadowban" .
to decode what might be happening here, lets lay out a list of possible reasons that could have lead to this:
1. algorithm cycles/drop in views, which can happen due to more competitors entering the niche, and mass spamming with multiple channels.
this will effectively reduce your views unless your quality is unique.
so to battle this, you can keep making more channels yourself and post the same type of content.
youtube gives a boost to freshly made channels.
2. it could be that you violated something that none of us are aware about and you aren't being honest about it. (i'm not saying you did it).
3. it could be that your channel's content does not meet the "quality standards" that youtube is expecting and during a manual human review, they may have flagged your channel as "spam" or "low quality" , and limited its reach.
you mentioned that you were using "stock videos" , in one of the replies here. this could put your channel into the "low quality" category.
this is because stock footage is considered as "re-used/repost" content, which you don't own.
the days of easy repost content spam is over. you can get flagged.
youtube keeps running periodic reviews on channels to battle spam.
this is an example where youtube has accepted, limiting the reach of content:
4. if you botted or did anything blackhat, they could potentially limit you, and that is determined by the quality of the service or bot you are using.
since you said you haven't done anything blackhat, but i may take a reference from your original post which talked about this being another channel of yours.
if you run multiple channels on the same ip/device/email, expect to get limited as-well.
they can flag you for spam and limit your reach.
if it was that easy to scale, everyone would easily be able to make 100's of channels using the same ip/device/email and mass produce the same content type, publish them across all the channels and become millionaires.