In SPO there is one very useful OTB application layouts page groupstatus.aspx. Using this page we may redirect user to Notebook, Planner plan or Sharpeoint site associated with O365 group, e.g.
{siteUrl}/_layouts/15/groupstatus.aspx?target={target}
where {siteUrl} is url of the site associated with O365 group. And target may be "site", "notebook", "planner", etc. Full list may be found here: Generic URLs for all Office 365 Group connected workloads.
If we don't know url of the site associated with O365 group we may still use this page in context of the root tenant site and specify id of O365 group in additional query string parameter:
https://{tenant}.sharepoint.com/_layouts/15/groupstatus.aspx?target={target}&id={groupId}
In this case it will still redirect you to the requested target. And this is exactly how we use this page in TW - we open it in context of the root tenant site and provide target=site and id of the group in query string.
However at the same time Sharepoint has own redirection system for mobile devices: when you visit some Sharepoint site from mobile device it will redirect to special application layouts page optimized for mobile view \_layouts\Mobile\mblwpa.aspx (see Overview of Mobile Pages and the Redirection System). According to documentation this redirection for mobile devices is performed via http module (SPRequestModule). It means that in ASP.Net pipeline it will happen before request will come to groupstatus.aspx page. So when we redirect user to the root tenant site on mobile browser:
https://{tenant}.sharepoint.com/_layouts/15/groupstatus.aspx?target={target}&id={groupId}
Sharepoint will just redirect user to mblwpa.aspx page in this root site
https://{tenant}.sharepoint.com/_layouts/15/mobile/mblwpa.aspx
and instead of seeing site associated with specified O365 group - user will see root tenant site. Will try to report this problem to MS using available communication channels. For now posted this problem on StackOverflow here.