WiFi problem

We brought WI-FI router RB912UAG-5HPnd-OUT and now we have some problem with this product. I configure it as bridge and connect to 2.4GHz Wi-FI router. But when i start to test this configuration, i can see that ping to my Mikrotik router is very unstable. I decide that it’s problem with missed Wi-Fi antenna, but now 5 GHz wi-fi antenna is added and situation can’t named perfect. When i ping RB912 i receive long ping and (very rare) packet lost. Notebook placed in 2 meters from router. Does anybody have some theories why it can happen?
P.S. Sorry for my non-good English

Probably too high signal levels.