Currently the default_activity_completion.feature uses the name ("Add requirements") to identify the data field for mod_assign, which is fine if mod_assign is the 1st module.

In case another module plugin precedes mod_assign alphabetically (e.g. mod_aspirelist)  the data field name refers to the wrong data field and the test will fail with the error

TypeError: rect is undefined (Facebook\WebDriver\Exception\UnknownErrorException)

This can be fixed by using the ID to identify the data field instead of the field name.

Line 33 of completion/tests/behat/default_activity_completion.feature should change from 

| Add requirements | 1 |

to

| id_completion_assign_2 | 1 |  

To recreate the issue:

Install a vanilla Moodle 4.3

Install master branch of mod_aspirelist from https://github.com/tonyjbutler/moodle-mod_aspirelist.git

Run core Behat test for completion/tests/behat/default_activity_completion.feature

You should see the aforementioned error.