for a freeze to happen you don’t have to mark all regions in a track beforehand. There is allready an open issue about freezes causing a crash: https://tracker.ardour.org/view.php?id=9539
In my experience freezes do actually work most of the times until they don’t. I couldn’t narrow down the circumstances of failure so far.
In your specific case: Does the freeze also lead to crash when you just right click on any of the regions and call the freeze function without having both marked beforehand?
That is different from the case i encountered last time. For me the process was stalling after around 90% and then crashed.
I just went back to the session where this occurred on a track with multiple regions.
Here are my findings:
The crash only happens when i am in grab or in stretch mode, i.e. when i right click with the mouse over one of those regions so that it automatically gets selected. It also does not happen when i right click over an area with no region, i.e. after the end marker.
We have a convention and have had a convention for many years that undo only applies to changes to the timeline. Since freeze requires altering plugin/processor state, the operation cannot be a part of the “undo” system.
Having a separate undo/redo history for signal routing/mixing/processing has been a long term goal for … a long time.