Comment by snsr

Apparently a 1.5mm puncture due to a meteor/debris strike in the Russian Soyuz MS-09 module.

More information:

http://blogs.esa.int/alexander-gerst/2018/08/30/slow-leak-de...

https://twitter.com/RussianSpaceWeb?ref_src=twsrc%5Egoogle%7...

http://www.russianspaceweb.com/soyuz-ms-09.html#leak