Xcode 9.1 source code completion not working

I've been facing the following issue since XCode 9 -

The source code completion does not work in a nested level. Eg:

for i in 0..<5 {    //works fine when I start this look in a function body
    ..
    ..
}

but here is where the issue occurs -

for i in 0..<5 {
    ..
    // code completion does not work here. none of the following are completed - for loops, while loops, do-catch, if-else, if-let
}

And its not just happening inside for loops. I see the same code completion failure inside while-loops, do-catch and if-else. The code only completes while typing in the main function body ... not within any code block.

Is this due to some auto complete setting? Or a bug in XCode 9 onwards?