I own a Galaxy S10 plus with 2 wireless "FAST" chargers, no matter which one I use they both will show week charging detected when in use. They will only charge about 10% in a 7 hour period. This phone is only about 3 or 4 months old, original phone purchased was returned for a new one both phones have done the same the thing. The fast chargers worked fine with my old S7 active.
What is the problem?
What is the solution?
Not so fast!
I remove the case, the 1st night the phone charged from 40% to 100%. The 2nd night the phone charged from 40% to 52%. Both nights it sat on the charger for over 7 hours.
I would try a different wireless charger at night. It could be that the wireless charger is shutting down. It is also possible that something is bumping the phone and causing it to be misaligned with the charger.
If you can post a picture of the Settings -> Device Care -> Battery -> "Battery usage" screen that could provide some clues.