"Light Leak" / Bezel Separation example picture
Here is a Google Spreadsheet with all the responses so far:
Google Spreadsheet
Data Analysis via PowerBI (thanks to /u/Cranberry_Dense):
PowerBI Data Analysis

tl;dr:
Units manufactured in June 2020 are most affected by the light leak issue, July the least and May 2020 is in the middle. The issue appears to have been fully fixed for units manufactured August 2020 or later.
There is a picture floating around showing a new FB01 version, however even in October 2020 FA01 is still manufactured and the standard.
Reading out the manufacturing date from the serial number is possible (see below). Since the serial number is also printed on the outside box this makes it useful for local shop buyers to pick out an unaffected unit.

Hi everyone,

I wanted to open this thread to collect information about the Odyssey G9 in terms of manufacturing date, version number and whether the bezel separation / light leak issue is present on your model.
To check for light leak (example picture):

1. Turn off all light sources in your room, make it as dark as possible.
2. Turn up brightness of the monitor to 100.
3. Now display a white image.
4. Check whether at the top between bezel and panel there are any gaps where light is leaking out.

Template for your post:

Model code: 
Version Number: FA01 / FB01
Manufacturing Date:  May / June / July / August / September / October 2020
Light Leak present: Yes / No (opt. position top left, XXmm length)
Ordered/Received date: 
Retailer (Country)

To find out your manufacturing date:

• for the US/CA LC49G95TSSNXZA model just check the back of your monitor, the date is listed there:
  https://i.imgur.com/sesx7WW.jpg

• as an alternative method you can check the 8th and 9th digit of your serial number (Source 1, Source 2), where the 8th digit stands for the year (2019 = M, 2020 = N) and the 9th for the month (5 = May, 6 = June, 7 = July, ..., A = October, B = November, C = December)

As an example:
https://i.imgur.com/LAvgGO2.jpg
The 8th and 9th digits are "N7" here, so the manufacturing date is July 2020.

Taking the unit from /u/iiSeptum as an example then, please post here something like this:

Model code: LC49G95TSSUXEN
Version Number: FA01 
Manufacturing Date: July 2020
Light Leak present: Yes (top left, 40mm length)
Ordered/Received: 11.08.2020 / 25.08.2020
CCL Computers (UK)