Javascript "once is not a function" errors after library include
I had this happen in my custom module as well. I then noticed it worked when logged in but once I was unauthenticated my code would throw this JS error. In the end it was simply an issue where I needed the dependency you listed already in my custom module library file dependencies:

dependencies:
- core/drupalSettings
- core/jquery
- core/jquery.once


Once I added this the required JS file was included when unauthenticated as well.

For a little extra information that forced the following JS file to be included as well:



It looks like you solved your specific instance which ended up being multiple versions of jQuery being installed. I would avoid that if possible as it complicates things a bit.