When i choose color and then click on an object to paint it, then it works usually, but sometimes it just doesn't. 

I think it's more likely to not work for roof objects in Buildings section. If it doesn't work once, then it never works on this object, no matter how many times i click. However clicking from other sides does work. 

Also after painting operation failed for one object, there's a chance it might not work on other objects, at least for some time. 

That's all the information i was able to collect 

Hey, thanks for reporting this! I've not been able to reproduce this issue so haven't found out yet what's going wrong. If you, or someone else finds a way to reproduce this I'll look into it.

I thought I had this issue, but I figured out you can not paint on every block.  Sometimes you need to create a new material and then you can paint the block.  
I'm not sure why, I came to the forum to research this behavior.  Is this a bug or an intended feature?

I'm running the linux flavor of the software.

I think the problem is resolved, after using the software a bit more, I no longer get the issue.  Maybe it was user error, when I first tried Asset Forge I might have confused it with my stumbling around trying to figure things out.

If you delete a group of blocks, then restore them by Ctrl + Z. Sometimes the blocks are not pressed and are not painted.

1) Assemble a three-story house.

2) Color it.

3) Remove the second and third floor.

4) restore by pressing ctrl+z.

5) Try to color the blocks on the restored floors.

some are not colored, the cursor does not see this block.

If you rotate the camera for a long time, sometimes the error disappears.