WRT1900AC ver1 poor wifi performance

Hi everybody
So I used last version openwrt 18 ...
My goal is to use a pppoe isp connexion in WAN and a second ISP router providing
I setup the second wan in vlan 3 , install load balance software
When I test my wifi connections 2,4 and 5 - both are very poor speed . I try chose different channel etc .... and nothing change
As a test I obeserve with factory software using wifi download is 80-100MB and with openwrt cable I have 30-45MB on wifi no more that 17MB

Anyone have more information how to fix it ? or is just like that ?
Thank you

The speed tests are in both cases with both ISPs enabled?
Is it the same with wired PCs?
I presume that you are following the exact same steps when testing the speed in both cases, that means same channel, same client, same program, same distance from the router etc. Is that correct?

Yes , I tried testing in different ways
As a conclusion , I can tell you one of the main reason is using mixed wpa and WPA2 encryption for WiFi
I chose only WPA2 and now with both ISP I can have on Speedtest 300 for downloading and 260 for upload
Also Speedtest say that I have multiple connection

Thank you , I figure out , was from ipv6 when I was enable it

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