How easy is it to lose permissions in 'public' schema?

[Rob Sargent <robjsargent@xxxxxxxxx>]

    I'm using postgres 14 in a database recently
      brought over from postgres 10.  (I did not do the bringing over.)
      
      In my set-up, I partition datasets by schema, create a role per
      schema and part of that is this explicit permission granting (from
      superuser):
    
> p\g
>         grant all on all tables in schema base, bulk, sgstemplate to
>         sgstemplate\p\g
>         --where sgstemplate is sedded to the real deal by the installer
>       
    there is no explicit 'public' in that set-up
      and here-to-fore the new grantee has been able to see into public
      stuff just fine, in particular to public functions which rely on
      getting grantee's version of tables (replicated in sister schema).
      
      I've just bumped into this.
    
> barnard=> select
>         public.genome_threshold_mono('a'::text,'b'::text);
>         ERROR:  permission denied for schema public
>         LINE 1: select
>         public.genome_threshold_mono('a'::text,'b'::text);
>       
    I know I haven't intentionally removed
      'public' from grantee's purview and short of the code block above
      not actually getting run, any guesses as to how access to 'public'
      got removed from grantee?
      
      
      I've run those grants specifically naming public and all is well. 
      Do I need to add that to the installer script?