Steps:
1. Open attached project
==> All the scripts (reside in 4 different assemblies) have compilation errors
==> You will see two compilation errors come from assembly '1' and '4' in console
2. Fix the compilation error in 'T1' script from '1' assembly
==> You will see all the remaining errors in the console (can be a bit different result, depends on the time you are looking into this issue)
3. Create a new folder
4. Add Assembly Definition file into it
==> All scripts are recompiled (Ok)
==> You will see only one error in console now, error comes from '4' assembly.
5. Fix all the issue that are shown in console - one-by-one - until console is empty from errors
6. Take a look into solution scripts
==> The 'T2' script still has a compilation error

Please, take a look into attached movie for details.
Dependency graph in project is shown in attached image ('dependencies.png').

Not a regression
Also repro in Version 2018.4.8f1 (9bc9d983d803)