@Beckenpol Hi, my pleasure if I helped any~ For your situation, I am afraid that there is no chance for you to make full use of the range extender.

@amalac Hi, thanks for posting question here. To assist you efficiently, I've forwarded your case to the TP-Link support engineers who will contact you with your registered email address later....

@Patar Hi, to assist you efficiently, I've forwarded your case to the TP-Link support engineers who will contact you with your registered email address later. Please pay attention to your email box...

@AF63 Hi, to keep stable network performance, I am afraid that Archer BE400 can not afford 200 clients.

@smundu Hi, thanks for your update. How many Decos do you have? It is suggested to share their hardware here, and update firmware to the latest. What kind of clients do you have? Thanks for your...

@Ettan Hi, thanks for posting question here. If it is firewall problem of Deco M4, I am afraid another two ports you set up will not work, either. You may follow this guide to check your settings...