I was facing similar issue with version 8.x-3.12 when I was adding any string...

I was facing similar issue with version 8.x-3.12 when I was adding any string in the Lat/Long fields as soon as focus was going out of field input, it was changing to NaN. And on submission it was giving same issue.
In code, parent set value was being called before the custom code execution. After changing the order of execution it started working for me. I have attached my patch below.