lake update gets stuck if I add mathlib as dependency

[lattice0]

When the last 2 lines are added:

import Lake
open Lake DSL

package "lean1" where
  version := v!"0.1.0"

lean_lib «Lean1» where
  -- add library configuration options here

@[default_target]
lean_exe "lean1" where
  root := `Main

require mathlib from git
  "https://github.com/leanprover-community/mathlib4"

then I run lake update -vv and it displays no output and gets stuck forever with no return.

[LordGoatius]

I've gotten the exact same problem trying to add Mathlib. - -vv gives nothing and strace shows it freezing at this point:

I'm just starting with Lean, so I'm not sure where to start with this.
My lakefile looks like this:

import Lake
open Lake DSL

package "PlanePartitions" where
  version := v!"0.1.0"

lean_lib «PlanePartitions» where
  -- add library configuration options here

require "leanprover-community" / "mathlib"

@[default_target]
lean_exe "planepartitions" where
  root := `Main

The manifest appears unchanged after each attempt.