S24 Ultra fast charging unstable / PD issues after Dec 18 security update

[Irrelevancc]

Charging behavior changed immediately after the Dec 18 security update.

When plugging in USB-C PD cables (tested with Apple 20W and Samsung fast charging block and a PD dual charging block):

Initial estimated charge time is normal, but fluctuates wildly (1h 47min → 4–5h → back)

Phone briefly showed reverse charging behavior even when no device was connected to output

USB Debugging affects charging estimates

At high battery percentages (80%+), estimates stabilize but remain inconsistent across chargers

Normal charging curve (taper at 80–100%) observed with both chargers

Steps Tried / Workarounds:

Tested multiple USB-C and USB-A→C cables

Tested multiple PD chargers

USB Debugging on/off

Default USB Configuration set to “Charging only”

Restarted device

Is this a known issue?

Any recommended fix or firmware patch coming soon?

Has anyone else experienced similar behavior post-update?

[MarvinMod2]

Turn off fast charging, turn off phone, put on charger. Turn on phone, after full boot, unplug, turn fast charge back on then test.

[Irrelevancc]

Ive tried that and it didn't work. I've tried different chargers, cables, and still get the same result.

[Toshiro47]

Similar issue after update. Phone claims to be Super Fast charging but takes 20 minutes to charge less than 10%

[Irrelevancc]

I sort of fixed it. What you need is a USB C to USB C and a C only charging block. Not a charging block with two sockets. You need a plain simple singular USB C socket. After a while of doing that the issue slowly disappeared. Its not instant but you will definitely see the progress.

[Toshiro47]

This is very interesting. I am curious as to why! Are you using a 25w charger then?