Definitely pay attention to Matti Haveri's point about using an external hard drive! See this:
Move your Photos library to save space on your Mac - Apple Support
If you're not using an external drive, where is your Library? Is it in the Pictures folder?
How did you import the pictures? I ask, because "Imports" can bypassed by certain methods of import, so there's not test for duplicates, so it's possible though unusual, that not all pictures appear in Imports. Library shows all your pictures according to their metadata "create" dates which can be wrong and totally haywire. Recents is the place to look for recently imported pictures. In Recents, the pictures are always in order of date added. It's good to have something you can depend on!
Of course, you should look in Recently Deleted (in case you accidentally hit the wrong button) and in Hidden (same reason.)
Have you tried re-importing them? The Import routine will tell you if they are already there. And you could try importing some test pictures to see if they work.
Let us know-- we might come up with other suggestions...