Why is my MacBook Air losing power while charging?

I don't quite understand your question, though I surmise your Mac is consuming power in a manner inconsistent with your expectations.

• To charge your MacBook Air read Charge your MacBook Air or MacBook Pro - Apple Support.
• If it is not charging read If your Mac battery won’t charge - Apple Support.

With Optimized Charging enabled (that is the default setting), then macOS will periodically drain the battery from 100% to 80% in order to exercise the battery to maintain better battery health.

If battery charging is paused or on hold on your Mac - Apple Support

https://www.macworld.com/article/2217188/macos-optimized-battery-charging-system-settings.html

"Why is my MacBook Air losing power while charging?: My MacBook Air is loosing power even when plugged up. Is there a cord that can power it or not ?"

-------

Mac Not Charging:

If indoors, flip the switch for the plug on the wall so that there is power to it, and see if that fixes this. It might just be as simple as that. If nothing else works on that plug, then you may need to check the circuit breaker panel, and see if you need to turn it back on.

Check your wattage for your charger. It should be AT LEAST 20 watts. maybe your using it during its charge (the fact that you know about the battery discharge infers that you are using it during charge)