my app icons randomly become smaller and then become bigger

This is a bug wthin iPadOS14 - of which we have seen frequent reports in the Support Community. The issue of inconsistent scaling/sizing of Home Screen App/Folder icons also extends to the new-style Widgets - whilst the old style Widgets are seemingly unaffected by this bug.

The iPadOS 14.0.1 update appears to have resolved this issue for the majority of users. If you have not yet updated to the currently supported version, you would be best advised to do so - as the update addresses a number of issues.

If you have already updated - and the issue persists - a forced-restart of the iPad may be beneficial:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

I hope this information and guidance proves to be helpful in resolving resolving the problem.

can you tell me what iOS are you using and what device are you using? that will help m solve the problem, since was it the new iPad air 4?

This happened to me but when I completely powered on and off my iPad it has not reoccured.