[BUG] 380.57 - Latency issues and packet drop WiFi to WiFi only

Hello,

I encountered a strange problem using Asuswrt-Merlin 380.57 on a AC66U and N66U. I am experiencing connectivity issues between WiFi devices only.
So this is what happens when I ping on both routers, 2 Ghz or 5 Ghz WiFi:

Wireless Device -> Router IP: perfectly fine ✓
Wireless Device -> Device connected to router on Ethernet port (both 100M and 1000M): perfectly fine ✓
Wireless Device -> Internet IP: perfectly fine ✓
Router -> Wireless Device: perfectly fine ✓
...
Wireless Device ->...

[BUG] 380.57 - Latency issues and packet drop WiFi to WiFi only