I was using Vivaldi on a Pi4 for editing a 2.1.1 instance and had hidden a couple of tabs.
I was trying to do some text to speech stuff and Vivaldi doesn't support it so switched to editing in Chromium and was surprised that my hidden tabs re-appeared. Opened it up back on my Win10 machine and hidden tabs were un-hidden
Is the hiding tabs just on a per session type basis or is this a little bug
Yes it's per browser. It is a question we are thinking about... For example I wouldn't really want people sending (or cut/paste in the forum) me flows with hidden tabs that could easily do malicious things on them - unless I remember each time to go and unhide everything. So yes at the moment it's how you set up your working session.