**Steps to replicate the issue** (include links if applicable):
* open a private window
* go to [m.wikidata.org](https://m.wikidata.org/) or [test.m.wikidata.org](https://test.m.wikidata.org/)
* follow the “log in“ link in the sidebar, or directly go to [Special:UserLogin](https://m.wikidata.org/wiki/Special:UserLogin) ([test version](https://test.m.wikidata.org/wiki/Special:UserLogin))
* enter your username and password, submit the form
* if applicable: enter a 2FA code, submit the form
**What happens?**:
* I end up on https://www.wikidata.org/wiki/Special:CentralLogin/complete?token=redacted or https://test.wikidata.org/wiki/Special:CentralLogin/complete?token=redacted (i.e. non-mobile site)
* there is an error: “No active login attempt is in progress for your session.”
* if I manually edit the URL to go to m.wikidata.org / test.m.wikidata.org (keeping the CentralLogin token intact), then I am successfully logged in there
**What should have happened instead?**:
* I should have been sent to m.wikidata.org / test.m.wikidata.org directly
**Software version** (skip for WMF-hosted wikis like Wikipedia):
* MediaWiki
** Wikidata: 1.40.0-wmf.1 (2fc21db)
** Test Wikidata: 1.40.0-wmf.2 (e31f436)
* CentralAuth:
** Wikidata: 4991334
** Test Wikidata: c94dd1a
**Other information** (browser name/version, screenshots, etc.):
* This may be related to other tasks like T225814 and T257852, but IIUC both of them are about “automatic” login (if you’re already logged in on the non-mobile site, and/or on another Wikimedia wiki?), not about “manual” login.