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6.1 was released over a year ago, so I'd highly assume that isn't the issue.
Are you using an official/known brand? Both the cable and plug need to support 25W charging.
Make sure fast charging is enabled in settings.
Go to the Samsung Members app > Support > Diagnostics. Any issues?
Simple soft reboot- hold power and volume down until phone restarts.
Clear cache partition.
Make sure port is free from debris.
Worst case may be time to contact customer support