Which firmware are you using DDWRT or Stock firmware.
What is distance between your wireless client and R7000?
Check if the problem exists when using different channel.
Website security can be a complex and even confusing topic because of its ever-evolving landscape, for that reason, it’s important to keep in mind that security (especially website security) is never a set-it-and-forget-it solution.
Why is website security important?
Try R23310, it worked for me with DHCP issues.
http://www.desipro.de/ddwrt/K3-AC-Arm/r23310/
Which firmware are you using DDWRT or Stock firmware.
What is distance between your wireless client and R7000?
Check if the problem exists when using different channel.