To reproduce:
1) Create a new project
2) Create two sprites in Project Browser
3) Rename them outside of Unity (through Files, for example) so that they're the same name, just with changed case (for example, "square" and "Square")

Expected: Unity either displays one of them or renames it automatically to avoid the identical naming (as OS'es like Windows don't support it)
Actual: An infinite loop is made as it tries to import the two objects. If you rename one of them in Files to break the loop, the project browser is flooded with garbage until you do "Reimport All"

Reproduced in 2019.3.0a1 (although it's much slower here), 2019.3.0b8, 2020.1.0a1, 2020.1.0a11
Not reproduced in 2019.2.5f1, 2019.2.11f1