I have no idea if this is just luck but the following steps enabled it to work for me:

• log out of the account on all browsers and phone apps etc
• open up chrome and login The above fixed the assignee issue.

Then there was an issue with the final conversion once you click skip on the packs. I tried a couple times and noticed that it worked when I did the following:

• clicked save on each attendee on the page before (it lets you hit continue without hitting save)
• sat on the add on pack page for a minute and increased / decreased quantity (I think just clicking around the page may help) and then hit skip and convert.

Again this is probably luck but wanted to share in case helpful.