Mikrotik hAP ac^2 - network requests losts first few minutes after connection to LAN

Hi,
I’m kind of newbie in RouterOS world.
I did an initial router setup and I have already long time troubles with some devices connected to network (notebook, phones, …) that some network requests are lost. This happens a few minutes after the connection to network via WiFi. Then it seems like router start to believe the requests and all start to work.

I have checked the firewall rules and was checking the counters but I didn’t find any connection between the requests and some of the rules dropping the packets. I also tried to disable the rules step by step and it didn’t help.

Firewall rules is a predefined set. (see attachment)

Can you give me some hint what can cause such behavior?
Thx a lot.
FirewallRules.PNG

What you mean by network requests are lost? What problem are you facing exactly?

You mean your devices connected to wireless interface and gonna wait for few minutes before it started to work? Or the connection will stop working after few minutes?