Construct 2 does not keep an error log. Even if it did, it might not include any information about the problem, and even then if it did, it might not be enough information to allow us to actually fix anything. To actually be able to fix bugs, we need all the information required in the bug report guidelines, the most important being reliable steps to follow to reproduce the issue. We may need to follow the steps to reproduce a dozen or more times before we even understand the problem, so without these, it's almost impossible to make any progress.
FWIW when you save a project, Construct 2 takes the following steps, specifically to try to avoid issues like this. Suppose you're saving to project.capx. It never writes directly to the file. Instead:
1. It writes all files to a temporary folder
2. Assuming that was successful, it then compresses it all to a zip (capx files are just renamed zips), to a file named project.capx.tmp.
3. Notice at this point, it still hasn't touched project.capx at all, and only continues if everything so far has been successful. Now it deletes project.capx, and renames project.capx.tmp to project.capx. This basically swaps the old file for a new fully-saved one.
There are several types of problems this avoids:
- if writing files to a temporary folder fails, project.capx is untouched.
- if compressing a zip fails, project.capx is untouched.
- if deleting project.capx fails, it's left behind.
- if deleting project.capx succeeds but renaming project.capx.tmp fails, you should still have a valid project file at project.capx.tmp which you can rename and use.
The only case I can think of that actually completely erases the project is if renaming project.capx.tmp fails and somehow deletes the file, which is a catastrophic OS/file system/hardware failure. These types of errors can happen on any device, and this is why you need to have a good backup strategy for any kind of digital work you do.
BTW even if you save a project folder, each individual file in the project goes through the same process as above. It's designed so there is as little scope as possible for any work-destroying bugs. But they can still happen due to factors outside our control.