Everybody who has ever tested early a new version of a software knows that it implies some risks. Though it may occur rarely, the risk is always there for your device. For the beta version of iOS 10, it seems that you might end up getting locked out of the Apple account if you test it. Several beta testers have reported that they could not reset their passwords and that they were locked because of security reasons.
Maybe the worst part of this was the fact that nobody knew what is the source of the issue. However, it seems to be tightly related to the fact that the users had enabled the two-step authentication feature. Apple Support, on the other hand, cannot reset their passwords manually if they have the particular feature enabled. What you can do though is to request an account recovery, but this might take a few days or even more, since you have to prove your identity.
This problem has also been reported to appear for those who have been using the 9.3.2 version and the 9.3.3 beta one. This might hint to the fact that it’s not the version to blame, but a different error somewhere else. As such, you might not want to be the first yet to test the tenth version of the software, since all reports show that it still has lots of bugs and unfixed issues. The last and official version is expected to be released this autumn. You should stay tuned for more updates on issues with the beta version and more details about the official release of the new software, to be sure you won’t miss anything!