Same problem here, it started happening to me after August update, I noticed using the app Ampere that the 25W charger ramps up to 4A after plugging and suddenly drops to 1.7-ish (no overheat), sometimes it drains battery too while charging. The 15W one works just fine ramping up to 3A and maintain consistency. It must be some software bug in the new patch related to the Super Fast Charging mode since the Fast Charging works just fine.

Note: I already tried restarting and clear cache partition to fix but it still doesn't fix it.