The devs have recently done some improvements on the AARs, which looks like it has come with some unintended consequences. If you could provide screenshots, as well as your username, MCID and what browser/channel you are playing on, I'll bring the example forward.
Can confirm the same issue.
The entire mission window seems to freeze up. So its not just selecting ARRs, but also dispatching units as the act of selecting an ARR can cause it to freeze up. Then when it finishes loading/un-freezes, it goes back to working fine
Username: Morvran
Version: UK (I know technically the wrong forum, but seems to be affecting more than just the US version at the moment)
Browser: Chrome (with LSSM)