Database issues when adding GUI

This is an unusual message and I hope someone(s) here can offer insights
into the cause of the problem I've been wrestling with for the past couple
of weeks.

Context: For the past decade I've run my business tracking database from the
psql shell (currently with postgresql-12.2) and decided it's time to add a
frontend so it's a stand-alone desktop application. I'm learning to use
PyQt5 as the widget set and application framework.

The database contains three lookup tables: activitytypes, industrytypes, and
statustypes, all have a single column and few rows. So I've started with
these to get python3 and PyQt5-5.13.2 to run the SELECT query and display
the results in a QTableView.

The problem with all three is that my code produces an empty window and
hangs. There's no python error displayed and the application reports finding
the database but not the tables. For example, the activitytypes debugging
log contains:
INFO:root:found database
DEBUG:root:Defining model/view
DEBUG:root:model error: Unable to find table activitytypes
DEBUG:root:about to execute select query
DEBUG:root:End of Program

I, and others on the python and pyqt mail lists and stackoverflow, can find
nothing wrong with the python code. This suggests it's something with the
database itself. But I have no idea where to look. The database structure
is:
bustrac=# \d
List of relations
Schema | Name | Type | Owner
--------+---------------------------+----------+----------
public | activities | table | rshepard
public | activitytypes | table | rshepard
public | industrytypes | table | rshepard
public | locations | table | rshepard
public | organizations | table | rshepard
public | organizations_org_nbr_seq | sequence | rshepard
public | people | table | rshepard
public | people_person_nbr_seq | sequence | rshepard
public | projects | table | rshepard
public | statustypes | table | rshepard
(10 rows)

What might stop a front-end application from finding a table that has been
readily accessed from the psql shell?

All suggestions and recommendations are needed.

TIA,

Rich