I have tried updating my local  <nixpkgs> directory with 'nix-channel
--update'.  

No change; the full nix-instantiate command does not terminate.  

The git commit of <nixpkgs> (in /home/paul/.nix-
defexpr/channels/nixpkgs/.version-suffix) is now 497e6d2.

Also, if I remove '--strict' from the nix-instantiate command I get:

<?xml version='1.0' encoding='utf-8'?>
<expr>
  <derivation>
    <repeated />
  </derivation>
</expr>

Terse##SELECTION_END##! but at least the process completes.

I have noticed that the non-termination problem is not confined to the
opencascage_oce package.  If I try 

$ nix-instantiate --strict --eval --xml -A guile /home/paul/.nix-
defexpr/channels/nixpkgs

that does not terminate either.

Best,

Paul.