Ways that work can get lost

Hello folks,
I am new to Toon Boom. In spite of my habit of hitting the “save” command every few seconds. And-- I belive-- always saving before I quit Toon Boom Studio, sometimes when I re-open a file I learn that I have lost some of my work.
Now I wonder if this is happening when Toon Boom is getting buggy. For example occasionally some my key commands stop working. Copy/paste for example, and also the command “a” and “s” to advance or retreat one frame on the timeline.
When I’m really carefull I save a whole new version before I quit Toon Boom.
I use a Mac Pro.

Any comments or suggestions?

I’m responding to my own post. My co-worker tells me that ToonBoom Studio doesn’t do so well with non-vector art. I had imported an Mov into my Toon Boom file as reference. Now I’ll try to avoid that.

Thank you for posting the additional information for everyone’s benefit.