All my saved tab groups disappeared... AGAIN, even though I have clicked the £save tabs" box.

Just to confirm, saved & closed groups are moved to the All Tabs menu in the toolbar, so you can't see them there after some time, even after expanding any "Show all" etc.? (Saved & closed tab groups have "hollow" icons, as compared to filled ones for still open groups.) Tab groups might actually fail to restore after a crash, so they might have gotten omitted from the session store over time. You can try following this guide to try to restore an older snapshot: [[How to restore a browsing session from backup]] to see if it has any of your missing groups there. (The restore after crashing should be resolved in v158.0 going forwards.)