Crash on use of trim tool

Help! I am attempting to use the group ‘offset deck mask’ to trim the ends of the group ‘decking to trim’. Crashes every time. Can anyone propose a good solution?

In addition, the greyed out groups in the outliner no longer show up in the model. If selected from the outliner, I see the bounding box but no geometry. Really hope I can recover it.
Large Plinth.skp (2.7 MB)

I expect the crashing is due to your trimming shape running into the small holes in the planks. I’d get rid of those. You you want to trim the ends off the boards and keep the middle or do you want to trim out the middle which is what you’d get if you use Trim the way your model is set up?

The grayed out objects in Outliner are either hidden or their tag is turned off so they shouldn’t show in the model space. That’s the whole point of Hide or turning off tag visibility.