I don’t think there’s any world where realizing capital gains when selling long term holdings is not “private wealth management”. The circular 36 even explicitly recognizes that dynamic management of wealth is allowed (so frequency of transaction doesn’t imply professional status).
The one clear thing that might be a trigger is using external financing (e.g. loans).
By the way the Circular 36 is fairly readable (chapter 4 explains how they would decide and the weighting of the criterias).
Searching around there’s some fun jurisprudence, e.g. 2C_389/2018 - 2019-05-09 - Finances publiques et droit fiscal - Staats- und Gemeindesteuern des Kantons Luzern 2014, direkte Bundessteuer 2014; where someone actually wanted to get the pro status (they had massive losses), when they were doing 88 transaction per year with 5M CHF. But since they were losing money they obviously can’t be considered professional 
(because professional would seek a profit).