Organic Twitter Impressions Falling?

First time poster here. I'm new to the field after leaving journalism a few months ago. So putting myself at serious risk of sounding silly here, but would appreciate any help anyway.

Working for a small MarCom company doing some content marketing for a few clients. As part of the deal we Tweet out blog posts about once a week, while the clients also send other Tweets several times a week to daily.

I'd anecdotally been noticing that Tweet impressions were falling over the past few months. I made a point to check on it this week and found that with three separate accounts, each showed a definite downward trend beginning on about Feb 1. Tweet days, times, frequency, and number of followers have remained more or less consistent, yet Tweets are not reaching the same audience.

Hard for me to believe it's coincidental. So what's up: Am I not knowledgeable about how Twitter works and been messing things up, or has Twitter somehow changed the game? Seeing as how I can't find any articles or threads supporting the latter, I'm guessing it's the former. But drawing blanks as to what might be the reason.

Thanks