MacBook Pro battery drains when connected to AC power
There are two things that can be attributed to this:

There is a technical issue with your charger
The Battery Health Management feature (released in Catalina) can make it appear you have a charging issue.

Wrong charger
You are likely using the wrong power adapter; it's too &quot;small&quot; for your particular MacBook.  Your machine requires the 87W power adapter.
If you take a look at Apple's support document Find the right power adapter and cable for your Mac notebook under the USB section, you'll notice that all of the adapters from the 29W that charges the MacBook to the 91W that charges the 16&quot; MacBook Pro all look identical so it's quite easy to mix them up. While you can plug in any of these into any of the MacBook computers (plain, Air, or Pro) and while it will &quot;charge,&quot; you won't get optimal results.

A &quot;larger&quot; charger can be used to power a &quot;smaller&quot; device.  In other words, you can use the 91W charger from the 16&quot; MBP to power/charge the 2015 MBA that only required the 29W charger.
A &quot;smaller&quot; charger should not be used to power a &quot;larger&quot; device.  While USB-C will negotiate the power being delivered, if the adapter cannot supply the requested current, it simply won't be there.

What you're experiencing is what's in the second  point.  The adapter is connected (and detected) but it simply cannot supply enough power to charge and for you use the computer at the same time.  If you notice, Coconut battery is reporting that it's charging with only 49W, yet the battery isn't charging.  You're likely using the 61W adapter. (That number is a misnomer because that current is what it's drawing from the power adapter current, not what's going to the battery).
Battery Health Management in Catalina
As of Catalina (10.15.5) Apple has implemented a feature called Battery Health Management that will stop charging and allow it to discharge to a predetermined charge (about 80%) before recharging again. This happens even while the charger is plugged in and working.
You can learn more about Catalina’s Battery Health Management feature in the Apple Support Document About battery health management in Mac notebooks
Therefore, assuming you're using the correct wattage charging adapter, this could be perfectly normal behavior.