Why Can't Top Find My Python Processes on Ubuntu?

See if you can get them using

ps -af | grep python3

Otherwise if the python code uses one of the os.exec*() calls, the same process continues but runs the exec'ed command which is the one you will see in top or ps. You can confirm this like this:

1. Start the command as a background process and recover its pid

   python3 [whatever}  & echo Python3 started as PID: $!
   

2. Use ps with the PID you obtained:

   ps -p $pid
   

With some luck you can even catch it "morphing":

#! /bin/bash

python3 {whatever} & pid=$!
for i in {1..10}
do
    ps -p $pid || exit 1
    sleep .2  # adjust for speed
done