According to at least one of the apps currently (roughly Friday midday UTC) Nauka is lagging the ISS by about 90 degrees
of longitude, central angle, which equates to about 10000 km or over 20 minutes difference in terms of time between them crossing the sky from a fixed observing point.
FWIW the vehicle has also carried out a couple of small engine burns and more are planned which would potentially introduce some small errors in observing predictions until the number crunching catches up with any changes in orbital parameters..
From Roscosmos:
” Thursday, July 22, 2021, the Nauka Multipurpose Module Flight Control Group specialists at Moscow Mission Control Center conducted two correction maneuvers of the module that had launched to the International Space Station the previous day.
The first maneuver took place at 15:07 UTC with the module engines burn for 17.23 seconds giving an impulse of 1 m/sec. The second burn for 250.04 seconds took place at 17:19 UTC with an impulse of 14.59 m/sec.
Orbit parameters after two burns:
- Orbital period: 90.17 minutes;
- Orbit inclination: 51.64 degrees;
- Perigee altitude: 230.43 km;
- Apogee altitude: 364.86 km;
Thus, the telemetry confirmed the module propulsion unit operability. Additional burns for further orbit correction are scheduled for July 23. The Pirs module is to undock from the ISS and deorbit on Saturday, July 24.”