eglSwapBuffers() taking so much time

Hello Arm Community!

I'm facing a problem with a HUAWEI P20 which has a GPU

GLES: ARM, Mali-T830, OpenGL ES 3.2 v1.r20p0-01rel0.9a7fca3f7dd712a473937294a8ae24b1

the Stramline/GA capture shows that eglSwapBuffers(), in some frames, are taking so much time to execute.

Why in some frames it's time is so low (like in the call 2) and sometimes very high (like calls 1, 3 and 4)?

Thank you very much!