Hey there,
Sorry to hear your predicament! I would begin with analysing your analytics from when you received the jump in views. There could be indications of whether you should revisit a theme that did well for your channel.
Using views as an indication of channel performance would not be my primary source. Instead I would have a look at the watch time and consideration compare the differences.
You can also look at the retention which will indicate how well you hooked the viewers.
Video duration also plays a big part. Has it changed or remained the same since the peak? I have tested reducing a channel from posting two 10 minute videos per day to posting one 30 minute video per day. It has exploded since.
But as another poster has mentioned already, there are also external factors to consider which may be playing a role in the dip.
The channels that you benchmark yourself against, have they been around longer than you? Are they your competitors or just random channels lol?
Finally, your titles and thumbnails may have been better around the peak. Have you tested for keywords that may perform strongly for your channel?
Hope even a tiny bit of this helps
Dave