The TD-W8980 uses an Atheros chip for 2.4GHz wireless and a Lantiq chip for 5GHz wireless. https://wikidevi.com/wiki/TP-LINK_TD-W8980_v1 The E900 uses Broadcom chips for wireless....

Check antennas are properly screwed on all the way til firm if you have a revision of the TD-W8960N with removable antennas.

If wireless co-existence is causing the D7s' wireless AP to only use one channel (20MHz) it could be the cause. W ireless co-existence is a software feature. Wireless co-existence is also sometimes...

It is an 802.11AC router it's just that the 5GHz wireless webgui settings leave a lot to be desired. I doubt it is an oversight, more likely Qualcomm Atheros or TP-LINK decided that said settings...

If the 2.4GHz is working then it can't a wireless button fault. The 5GHz wireless chip may be faulty so the driver isn't correctly initialising thus, driver isn't started and region isn't displayed.

The Archer C7 v1 is not wifi certified with no settings for wireless mode or channel width under 5GHz wireless in the webgui....