A6210 doesn't automatically reconnect after reboot

I have the same problem, although it is an A6200 adaptor connecting to an R6300V2.   I had been getting download speeds up to 45Mbps. My ISP after 3 service calls, said I needed a range extender. They installed an R6300EX, still getting 45Mbps.  The 4th service call they finally sent a tech that knew what he was doing. He tossed the extender(called “Default-5g_ext”) and instead of the mode being connected to 2.5Ghz, he changed the router to 5Ghz and we were getting up to 240+Mbps.
  
  When he left  My default router setting was pointing to the name “default-5G’  and he explained that there was another setting (“default-5g_5ext”) pointing to the range extender R6300V2.  On Win 10,  I did not previously have the problem with my D-link router.  I show 2 modes that my ISP configured. Originally because I was only getting download speed upto 45Mbps, they said I needed a range extender. So, I had them install a 6300EX, but still getting 45Mbps.  Finally, a tech came out that knew what he was doing and tossed the extender, reconfigured the mode from 2.4 Ghz to 5 Ghz, I was then upto 240Mbps.  Now this referenced problem. He left me with 2 modes called "Default-5g"-(connects at 240+Mbps)  and Default-5G_ext"-(connects at 45 Mbps).  When I reboot(or sometimes over night with no intervention) it switches back to "Default-5G_ext) at 45. I cannot find the "Default-5g" to even reconnect.  How (or can I) get rid of the 5G_ext?