I remember too there where problems with wifi in older kernels.
So i can only second sicelo too skip to a newer kernel.

But as long as postmarketOS still has trouble with wifi
https://www.youtube.com/watch?v=eux9IcB2lfg#t=80 and
leste currently uses "experimental" PowerVR patches,

a more safer start (imo) would be "known to work" devuan (4.15.7) kernel.
It may be worth trying a vanilla stable 4.18.16 too.
Happy hacking