Here is a sneak peak of the latest season data, it is all publicly available.

Season 17 once again sits in the bottom of the pack: (9-14th worst seasons of available data (first 5 seasons data is unavailable, so the list ends at 14)
S18 — 79.5%
S17 — 72.7%
S19 — 71.9%
S6 — 66.9%
S16 — 63.3%
S15 — 55.9%

Are you noticing a trend? Because I am. This is based on publicly available 7-day retention data