I can confirm that I am seeing the same symptoms on my Archer C50 v4.1 EU. If I place it 5 metres away from the laptop in the same room, I can't really connect to it any more on 2.4GHz. Changing the channel to 40MHz does seem to improve things, and I can now connect from the next room through one wall - but it is still not working at full power.
I have another TP-Link TL-WR841N with OpenWRT in the same position - and the 841N is showing 94% signal, while the C50 is showing only 72% signal - so something is definitely not working properly. On top of that, the C50 is the more modern device, with better hardware - so it should have even better signal than the 841N.
The C50 is on the 19.07.0 sysupgrade image.