How to troubleshoot a custom Gutenberg block error: “This block has encountered an error and cannot be previewed”

I’m using a plugin from LinkedIn Learning to customize into my own plugin’s custom Gutenberg blocks.

After I’ve edited the file plugin/src/index.js (I edited the edit() & save() functions), I now have:

In Microsoft Visual Code, I am running the process wp-scripts start which recompiles the plugin after every save I believe. This process originally found some syntax errors for me, but I receive no more syntax errors in the output of wp-scripts start.

In a local dev WP site, when I try to add the new block, I receive an error:

This block has encountered an error and cannot be previewed

At the same time as adding the new block, in the Chrome console, I see:

which I’m having trouble understanding.

I’ve set:

but there is no output on screen or in a debug log.

I’ve searched online for the error, and most solutions involve updating WordPress or disabling plugins. I only have Akismet & MainWP child, plus the plugin to produce the custom blocks.

Disabling Akismet & MainWP child does not resolve the issue.

How would I go about troubleshooting this error?

Help appreciated.