Based on the discussion on this forum thread: https://forum.unity.com/threads/prefabs-are-reimporting-every-time-a-code-change-is-made.939756

I was discovered that when the following conditions aligned, all Prefabs with a [SerializeField] attribute in a Script were reimporting:
1. Create a project
2. Create a Prefab (PrefabA)
3. Create a new Monobehaviour (i.e. ScriptA.cs)
4. Create another Monobehaviour (i.e. ScriptB.cs)
5. Add ScriptA & ScriptB to a prefab.
6. In Script A, add a private variable:
[SerializeField] private ScriptB scriptReference;
7. Add a new Script that contains this (AssemblyStaticInfo.cs):

using System;
using System.Reflection;
using System.Runtime.InteropServices;

[assembly: AssemblyTitle("AssemblyTitle")]
[assembly: AssemblyDescription("AssemblyDescription")]
[assembly: AssemblyCopyright("AssemblyCopyright")]
[assembly: AssemblyCompany("AssemblyCompany")]

[assembly: CLSCompliant(false)]
[assembly: ComVisible(false)]

[assembly: AssemblyVersion("0.0.*")]

8. Create a new script (UnrelatedScript.cs)
9. Modify that script, and notice that EVERYTIME UnrelatedScript is modified, PrefabA is reimported.
10. Remove the [SerializeField] from ScriptA
11. Notice the Prefab no longer reimports.

Expected: Unrelated code changes should not reimport prefabs.