Spurious message "stuck at solving universe constraint"

Prerequisites

Please put an X between the brackets as you perform the following steps:

• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

Consider the code:

example : Type := Nat -> Nat.

This might be partially written code being edited, to be continued with an attribute of Nat, or the dot at the end may be a typo.

The issue is about the error messages. Lean correctly reports

invalid field notation, identifier or numeral expected

but also gives an extra error message which seems spurious to me:

stuck at solving universe constraint
  imax 1 ?u.4 =?= 1
while trying to unify
  Sort (imax 1 ?u.4) : Type (imax 1 ?u.4)
with
  Type : Type 1

Context

https://proofassistants.stackexchange.com/q/4961/

Versions

Lean 4.20.0-nightly-2025-05-06 on live.lean-lang.org

Start with the minimal example : Type := Nat -> Nat. reproduced on live.lean-lang.org using the Lean nightly version from the report. Trace how diagnostics are produced for the invalid field notation and identify why the universe-constraint message is also emitted; done when the intended invalid-field error remains without the spurious universe error.