@Haydos Hey, I think the following link might be helpful: https://community.tp-link.com/en/home/stories/detail/1200

@Newtowork Your network setup is correct. Did you use 2*MR6400 to combine the bandwidth or to provide a backup connection in case one 4G band failed? You should also change Deco M4 into access point...

@M4-User I think your case might be the same as this one: https://community.tp-link.com/en/home/forum/topic/574532?replyId=1131052 It is the ISP customized version and you might also need to ask...

@Miyav You can't do that. it is only allowed two SSIDs on Deco. And they have explained here； https://community.tp-link.com/en/home/forum/topic/541930

@M4-User I think you could update your firmware first, 1.1.8 is quite old and they have 1.5.4 on M4 v2 now. Then please turn off fast roaming/ beam forming since your mobile device might have a bad...

@davporte Have you tested the MAC with a different network? Maybe you can try to update the software on the MAC first.