Russia Announces Its Annual One Year Launch Delay Of Nauka

Delivery of Nauka module to Baikonur postponed over fuel tank adjustments, TASS
“The construction of the Nauka module began in 1995. Russia initially planned to launch the Nauka lab to the ISS as a back-up of the Zarya compartment (the station’s first module that continues its flight as part of the orbital outpost) but the launch was numerously delayed. In 2013, the Nauka module was sent to the Khrunichev Space Center after metal chips were found in its fuel system. Rogozin said on December 16 that the module may be launched to the International Space Station (ISS) in early 2021 instead of late 2020 as was initially planned.”
Khrunichev Delivers Multi-purpose Laboratory Module “Nauka” to Energia, 2012