@basabeo You list a very structured approach to your training, but how you gauge your progress is trough a "body scan" wtf bruh, do measurements of your (neck, shoulders, chest, biceps, mid section, hips, ass, thigh and calves) + photos and calipers. I use this method:
https://scoobyswork.shop/body-fat-calculator/
What method you use for calliper's doesn't really matter, even if the data is incorrect, it will be consistently incorrect meaning you can track it.
I have a reminder on my reminders app every 2nd week to do this, and i write the shit down in notes, what applications you use doens't really matter as long as you record it, so every 2-4 weeks you compare data, and adapt and iterate. That said, there can be plenty of causes for your "muscle loss", the most likely culprit here is bad data..