I don't see a beta 4? Which router did you try this on?
It was just a build snapshot I pushed to Onedrive last night, from this post.
I'm currently compiling formal beta 4 releases to publish later tonight if all goes as planned. Due to the extensive changes done to OpenVPN certs management, another round of beta test is required.
One thing I noticed, when I changed settings and did a reboot from the gui, the router would sometimes not restart. It would just turn off.
Done a number of reboot these past two nights while testing things, no issue rebooting. Make sure it's not a plugged USB disk causing any issue. See if the system log contains any info.