I posted to this forum a few months back and also got in touch with TP-Link concerning this issue. I was told it was a bug and not an issue to worry about.

Here is the thread I started: Archer AX21-1800 v2.0 Led Controller INFO [1093] Start to run WAN0_OFF

After testing some more I can state that this IS an issue. It does disconnect the port. Plugging into one of the LAN ports does correct the issue, but that is a Band-Aid not a fix. Please look into why this is happening. I noticed that this has been discussed in other posts with basically the same response I received.