@theducks - the actual "trigger" for slowness in that beta version is any of these sorts of actions with multiple tabs open:
- Switching BV/CV/PV
- Switching tabs
- Find operations (which result in the above)
- Closing/Opening tabs
Does the slowdown still continue once you are back down to a single tab open (preferably not a huge merged one of course)?
Does the slowdown happen if you don't open any of those merged tabs at all - i.e. Open Sigil, immediately merge files in the book browser, and just work with a small number of other tabs?
You don't have a linux box to try the latest source on by any chance do you?