Why would the number of apps scanned be different?

[jugistrlayo]

Hi! Just wanted to ask:

So I use Malwarebytes along with Avast and Mcafee antivirus. 

Yesterday I did full scans on my Android phone using all three of these.

I've attached pictures of the results (top to bottom): 

Avast, Mcafee, Malwarebytes, all within a period of about 3 hours. Why would the number of apps scanned be different, as I didn't install or delete any apps between this time? 

Thank you!

[jugistrlayo]

Edit: whoops it changed the order of the images, it's Avast, Malwarebytes, Mcafee (top to bottom)