We've had trouble replicating this bug. I tested on a Motorola G4 with Chrome 59 and had no problems at all. We do not support Android browser (as it is old and unsupported by Google now), but we tested on an emulator for a Samsung S3 and didn't have this particular issue (had other issues with fixed positioning, but the menu still worked).
I don't think I can tell you how to fix it unless I can reproduce the problem and test it. Can you think of anything unique about the devices you're testing on that might cause this bug?