So, to summarize, don't trust those dates... perhaps if you are OK with eliminating some of the older data and having your model start on Jan 1, you may be able to get slightly more accurate dates on the charts, but otherwise, you can report this as a bug to Alteryx.

 

Better use the ETS and TS Tools with a pinch of salt. Currently, I got better results when I started my data with 1 Jan but still not a full blown solution.