Hi, this post is a bit dated but saved me lots of time. Thanks for posting!
It's 2020 and I'm still having issues with some versions of Android (tested on some models, not all, of Samsung and Huawei phones). Chrome version doesn't seem to change anything.
Luckily there is a solution other than disabling PCF. Babylon 4.1 (released yesterday) comes with cascaded shadow maps (see https://doc.babylonjs.com/babylon101/shadows_csm) which is almost drop in API compatible with the normal shadow map generator and doesn't suffer the same issue even with PC 🎉.
I'm guessing the underlying calls to webgl are a bit different and we happen to be lucky. Tip: if no shadow appears with CSM, remember to set your camera's maxZ value.
Hope this can help others