Age of differential

It’s still strange for me. Not only that situation make me confused, when I got fix, my antenna is over 3 metres, then when I walk under obstacles such as trees or roof, I got float (that reasonable), but when I got full sky view, it’s hard to get fix again, eventhough the green signal is more than 6.
In that condition, I try to changed the settig, such as, turned on the glonass AR. If not work, I increase the gps frequency to 10 and only use GPS satellites. Than I got it’s worked. But when I got float, I change again. But sometimes I couldn’t got fixed until morr than 15 minutes I think, or more over.

My questions, is there any condition when satellites signal is great, connection to base is great, but I still got float, in normal settings (AR glonass is off) and use 5hz?