intermittent Internal Server Error on webpage - activity log of diagnosis

My login to the server provides an overview,

Welcome to Ubuntu 20.04.2 LTS (GNU/Linux 5.4.0-45-generic x86_64)

  System information as of Sat Apr 22 23:49:00 UTC 2023

  System load:                      0.09
  Usage of /:                       70.8% of 24.06GB
  Memory usage:                     72%
  Swap usage:                       0%
  Processes:                        131
  Users logged in:                  1

I first confirmed disk utilization.

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            474M     0  474M   0% /dev
tmpfs            99M  1.2M   97M   2% /run
/dev/vda1        25G   18G  7.1G  71% /

I next looked at the error logs. When the error occurred, the fault trace ended with

  File "/home/appuser/app/controller.py", line 3424, in review_derivation
    dat = clib.read_db(path_to_db)
  File "/home/appuser/app/common_lib.py", line 142, in read_db
    for row in cur.execute("SELECT * FROM data"):
sqlite3.OperationalError: no such table: data
  

Probably a race condition in the Python? If so, this problem is due to my hack of writing the database to SQL. My motivation to resolve this issue is low because I had intended to switch to Neo4j. I haven't complete the migration from JSON/SQL to Neo4j yet.

I used top and saw 2 and 3 instances of gunicorn

I checked for redundant Docker containers running but saw only what's expected:

$ docker ps
CONTAINER ID   IMAGE                           COMMAND                  CREATED       STATUS       PORTS                                                                      NAMES
632ee101f714   v7_pickle_web_interface_nginx   "nginx -g 'daemon of…"   4 weeks ago   Up 4 weeks   0.0.0.0:80->80/tcp, :::80->80/tcp, 0.0.0.0:443->443/tcp, :::443->443/tcp   v7_pickle_web_interface_nginx_1
80bb13ec66ca   v7_pickle_web_interface_flask   "gunicorn --reload -…"   4 weeks ago   Up 4 weeks   5000/tcp                                                                   v7_pickle_web_interface_flask_1