Questions.... why did my profile go to %^&* as soon as I changed Battle Tags?

This is a serious question.

In the past year my win rate has been improving due to coaching and so forth.

2020 season 1. 53%
Preseason. 51.3%
2019 Season 1. 48.3%
2018 Season 4. 52%
2018 Season 3. 52.5

Then I change Battle Tags…
2020 Season 2. 47%
Current season. 30%

The moment I changed Battle tags I lost 12 in a row (from memory).
It was like the system was hunting for my MMR.

So the question is, WTF happened Bliz? The player didn’t change. My win rate since coaching had only been improving.

I am a point where I have to grind again and it is not fun at all.