OS V7. x - Hotspot work unstably

Dear all,

I had an issue when I set up hotspot on Mikrotik CCR2004 OS V.7 ( clients can connect to hotspot and access internet at first few minutes, after that, client couldn’t ping gateway although wifi connection wasn’t lost.
After I migrated from OS V.7 to OS V.6, the problem was over. What’s the best stable version of OS that I should migrated?

Thank you!