Graphic flickering in Android with dynamic vertex buffer updates.

I have 3 dynamic buffers with usage BUF_ShaderResource | BUF_Volatile VET_Short2N position VET_Color color and VET_UShort2N Uv.
They are used to render 2d sprites and get updated every frame.
I tested on very few devices and on gles emulator in editor and it presents some flickering to black at random intervals.
on my snapdragon 820 the issue is very relevant 2 or 3 black frames in rapid succession every 2 seconds while on snapdragon 625 or with the editor mobile emulator the flickering is far more acceptable but still present(e.g. a black frame every 10 seconds or more).
I also tried to rotate multiple buffers between frames with no luck.
In render thread I have a loop to read some custom commandarray so I first I lock the entire size of the 3 buffers at the same time as I don’t calculate the vertices for that frame upfront and fill all of them at the same time with my vertex data and then unlock them.
Do someone have experienced the same issue or has an idea about what is happening?
I don’t know if it may make any difference if I use some temporary mem to write my data and then lock memcopy and unlock the buffers just for the required size and one at the time instead of filling them directly all at the same time.