Wifi SSID changes on its own??

[chnapo]

I have 2 routers - one Mercusys MR30D serving as the main router and one older TP-Link serving as access point. Both provide a 5GHz wifi, TP-Link wifi is called "TP-Link_AN8BDI" and Mercusys wifi is called "Mercusys". The problem is that the SSID on Mercusys wifi will change to "TP-Link_" and it is a very curious problem, changing its own wifi SSID to a shortened name of the other wifi. Also to that new wifi, neither of the wifi passwords works. I set them manually to different channels (TP Link channel 40 and Mercusys channel 36), I live in rural area so there are no other wifi signals that would interfere, I made sure meshing is off. What could possibly cause the issue? Also, when I log into admin on Mercusys, it still think the SSID is Mercusys. The only way to solve it is to reset the router and then it will hold the SSID for a few minutes or hours, changing it later again to the same "TP-Link_". My Mercusys admin password should be very safe (it isn´t "admin" xD).

 

EDIT: Yeah, I can and will RMA the Mercusys router, but I am too curious and also don´t want to RMA if it is a config problem.