I also had this problem, and Juan's suggestion worked (Select Process > Modules > Install Modules, then click the Search button. The GaiaDR2 module should be found. Then click Install). I'm running Windows 10 64-bit. So this is not an uncommon problem.
I see. But we cannot reproduce the problem you are reporting on any of our working and testing machines, on any platform. On the other hand, many users, some of them also here on this forum thread, have reported that the new GaiaDR2 module was installed automatically without problems after the update on all supported platforms, including Windows 10.
This is a machine-specific problem that cannot be reproduced under normal working conditions, unless you can describe a specific scenario and a set of conditions where we can reproduce it consistently. Our update process is robust and works correctly on all supported platforms under normal working conditions, unless the contrary can be demonstrated.
From my experience, these issues are typically caused on Windows by antivirus applications blocking access to specific files temporarily. Other causes can be file sharing, backup and maintenance applications working as background processes, typically vendor-provided bloatware or poorly designed utility applications. We have seen also weird problems related to blocked, missing and corrupted files after buggy Windows updates. Note that this is beyond our control, basically because we cannot control what third-party applications do or don't do on your machines. FWIW, we use McAfee Total Protection exclusively on our Windows 10 machines, and we always maintain up-to-date clean configurations with minimal third-party software. Of course, none of our working and testing Windows machines performs any network activity besides strictly required software update downloads from trusted sources and file transfers within our intranet.
None of these problems exist on Linux (modulo outliers with wrong system configurations), and rarely on macOS.