Starting a new topic for this since the linked one is old.
Continuing the discussion from Mac Safari closes window when opening new tab:
@seren8 I have the same issue with Safari 15.4 and Monterey, and managed to track it down. It’s related to using Tab Groups with iCloud sync turned on.
When you’re in a Tab Group, if you open a new tab or click a URL, there’s a random chance it will go back a page or close the new tab. This doesn’t happen outside of Tab Groups.
The only way to fix this I’ve found is to either stop using Tab Groups, or turn off iCloud sync for Safari, but the latter was too much for me so I just stopped using Tab Groups.
I reported the bug to Apple using their form a few weeks ago, hope someone sees it (but I doubt it).
Tab Groups has all sorts of issues related to iCloud sync it seems, renaming a group is an exercise in frustration for example.