Hi @1339861mzb, thanks for taking the time to report this! Unfortunately this Phabricator task lacks some information.
Which web browser(s) did you test this with? Was this tested on a mobile device, or on a desktop device?
If you have time and can still reproduce the problem: Please add a more complete description to this task. You can edit the task description by clicking Edit Task.
Ideally, complete steps to reproduce should allow any other person to follow these steps (without having to interpret those steps) and see the same results. Thanks!

@Aklapper Done. Any other details should be mentioned? Regards

A list of steps to reproduce, step by step, would be welcome. It is way easier for others to try to reproduce. If I understand you correctly:

• Use Google Chrome on a mobile device (which Chrome version? On Android? Something else?)
• Go to the desktop version of wikidata.org (not sure how to do that, my mobile device would go to the mobile version)
• Log into wikidata.org
• At the bottom of the page, click the link to go to the mobile version
• Expected outcome: You are still logged in
• Actual outcome: You have to log in again

@Aklapper

• Use Google Chrome on a mobile device (Chrome version 78.0.3904.108 ,Operating system: Android 7.0; SM-N920C Build/NRD90M)
• Go to the desktop version of wikidata.org (go to the bottom of the page and click on desktop to go to desktop version)
• Log into wikidata.org
• At the bottom of the page, click the link to go to the mobile version
• Expected outcome: You are still logged in
• Actual outcome: You have to log in again

Any thing you think is still missing? Regards