Irregular ping times and low transfer rates, sometimes is caused by the scaling gobernor.
Setting the scaling gobernor to "performance" makes de cpu more active, an increases wifi performance. ( by defauls is set to "ondemand" )
In my case solved the problem. Orange pi may consume more power, but normally this is not an issue.
echo performance | tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor