d_williamson wrote: As suggested, I tried to set the question to mandatory in order to prevent users selecting "please choose" from the dropdown menu, and it still accepted the response without an error.

If a mandatory question is accepting the answer "please choose" as an valid answer, than this is a bug.
I recommend to create a simple survey to reproduce that issue. Then export is as LSS and attach it here or try in on demo.limesurvey.org.

Personally I would recommend a second installation on your own system to check issues with newer LimeSurvey version.

Thanks for that suggestion, I imported it to the demo site and get the attached error message (which does not occur on our local install), so I assume that updating it will produce this error message on our local environment.