It's not the size. 8Gb is fine. Ryzens are just a little picky about ram. Reason being is the cpu and ram work hand in hand, the faster the ram the faster the cpu. 1 stick of ram is serial feed, so all info transmitted is done so 1 bit of data following another. 2 sticks of ram is done in sync, first one stick, then the other, so speed of transmission is @ 1.5x faster than a single stick.
Think like a boxer throwing a jab with one hand. Has to wind up, swing, hit, pull back, swing, hit......
Now think using 2 hands, as 1 is pulling back, the other is already swinging. Hits are faster overall, even if the individual swings are just as fast as done by a single. Ram works the same way, as one set of data is transmitted, another is being prepared and ships out before the first is received.
Of course being Amd, that means the Primary slot for you is A2. The faster the cpu gets the data, faster it can work on it, but that speed is also set by ram speed, the Fclock internal timing is the same as your rams data rate.