Just in case someone is interested, here the official statement from TP-Link support: "This problem is caused by the design of router but not bug. I think the best solution is to set a static routing...

Hi, I have exactly the same issue on an Archer C7 V2. Did you find any way to fix this, or do we need to hope for a firmware update by TP-Link? Might it be working in custom firmwares like dd-wrt?...