Steps to reproduce:
go to a website in tab A, eg https://www.google.com/search?q=fsdasf
then, give it a child tab (tab B), eg cmd click first result
in tab B, cmd-click some more links, to give tab B some children
structure should look like this: 
then, still in tab B, close tab and reopen (cmd-w, cmd-shift-t)
observe sidebar saying multiple tabs left, but only can see one tab
toggling the show/hide children button fixes it
Expected behavior:
tab B and its children are present
Orion, OS version; hardware type:
Version 0.99.123.3-rc (WebKit 615.1.16.1)
MacBook Pro (macOS Ventura 13.2.1 build 22D68)
Image/Video: