I just got my S24 Ultra (SM-S928U) 3 days ago.  I have 25W USB C Super Fast Charger that I have been using with my S21 Ultra for 2 years and never had any issues with.  When I first charged the new phone on the day I got it, I believe it had about  ~50% battery and it charged without any issue.  However, I started having this issue when I tried to charge the phone this morning with ~17% battery left.  It kept getting disconnected and reconnected with charging icon at top right corner and remaining battery life in the middle of screen appear and disappear continuously.  I tried the following to figure out what the issue was:

- Plugged the same charger into another S24 Ultra with ~50% battery.  That another phone charged without any issue.

- Connected my phone to a laptop using same USB C cable. No issue with charging, just slow charging time as it was connected to a USB C port of an old laptop.

- Plugged non-super fast charger into my phone using the same USB C cable.  No issue with charging, and again just slow charging time (~2 hrs).

- Once my phone had ~30% battery, I plugged the super fast charger into the phone again and it stared charging without any issue.

It was clear that the charger was not the issue so I called Verizon customer service and spoke with a representative.  He advised that I should replace it with a new one so I went to the store and got a replacement.  I waited until the battery hit 15% and tried the super fast charger again and the same issue appeared.  So I used non-super fast charger to charge the phone until 20% (again, no issue with it) and tried super fast charger and it started charging normally again.

At this point, I don't think I will try to get another replacement again as the issue could be somewhat common with this model.  I am just going to make sure I always keep the battery above 20% whenever I charge it so I can use super fast charger.

I would appreciate it if anyone knows how to resolve the issue and/or workaround, if there is any.