Linksys EA6700 Router and RE6500 Extender issues

If I use my Linksys EA6350 as router and my Linksys RE6500 as WiFi-extender then my Sangean WFR-28D and IRC IKR1224WT Internet Radios are both ABLE to connect the WiFi network.

If I use my Linksys EA6700 as router and my Linksys RE6500 as WiFi-extender then NONE of Internet Radios are able to connect to the WiFi network. Both radios are performing an endless reboot cycle as can be seen in this YouTube clip.

Summary:
1) EA6359+RE6500: All devices are able to connect to the network.
2) EA6700+RE6500: All devices are able to connect to the network, EXCEPT for the Internet Radios.

NB_1! Both radios are able to connect to the EA6700 if the RE6500 is switched OFF.

NB_2! ALL other WiFi-devices like PC’s, Tablets, Smartphones, Printer and SetTop-box are able to connect to the network in any of the mentioned router/extender combinations.

NB_3! All relevant router and Extender settings are tested.

NB_4! The following firmware is installed. EA6700: v1.1.40.166281, RE6500: v1.0.03.006