I have just updated to the newest Lightroom iOS for iPhone 7 plus today.
The selective brush tool seems to leave a brush sized hole in the mask at the first point where one starts to brush in the mask. This does not happen on iPad. Otherwise the selective brush seems to work fine, except for the fact that the very first starting point does not become masked.
Is this just an iPhone 7 plus thing?
Running version 10.3.3
Having the same problem on my iphone 7plus.