@dbSoft 

Hey

Can you give us some more information on your setup, we don't really have enough to make any recommendations.

However my initial thoughts are that the APs you have deployed are 2.4ghz only, this frequency is easily saturated in almost all cases and depending on how many devices you have connected this could be congested.

Have you tried enabling AirTime Fairness on your SSID?

Its also worth noting that Roaming is not a solution to lag or performance, it simply offers better coverage and the option for more mobility.    Should all device be in one area, roaming will have no effect for you.

How many devices do you have connected?  What type of devices and what are you trying to accomplish?

  @Philbert 

Hello, I have two floors.

One ap on each floor.

2.4 ghz indeed. 4 devices are connected 

Xiaomi 9a android mobile.

I didn't tried airtime fairness.

  @dbSoft 

The 2.4ghz frequency is very congested in most setups so its recommended to use an app and scan for the best channels.   This is usually 1   6  and 11, as you are only using 2x APs 1 and 11 should be the best for you.

Setting the channel width to 40mhz is likely to help with the performance provided you don't have massive congestion in the airspace from other users...  20mhz is better for combatting congestion, but speed does suffer

I would try setting both APs manually to 40mhz widths, on channels 1 and 11 appropriately.   Retest that. 

If you do have a mix of devices   A  B   G   N etc then enabling Airtime Fairness is a good idea, personally I enable it as default on all 2.4ghz frequency as I find it helps with performance management overall.

What is your methodology / testing to determine that performance is an issue?   What are you seeing the effects?